Last One!

It's the last blog! My last entry will be a discussion about a masters thesis regarding the dexterity of forelimbs and the reason for this dexterity (Iwaniuk, 1997). The thesis is sectioned into several different research projects, all of which relate to the common theme of forelimb dexterity. The paper starts by defining the methods which will be used to determined dexterity, a scale method created by the author. He goes through and rates a variety of species. He then uses this data to determine which factors are influencing dexterity. This is what he found:

With regard to brain size, there is little relationship between larger brains and increased dexterity, the theory behind this being that evolution has more subtle ways of manipulating dexterity other than increasing the size of the brain. This makes sense. Many small animals (rats, lizards, squirrels) have quite a bit of dexterity for climbing, opening nuts, digging for food, and yet their brain size is constrained by the size of their skulls.

The second factor analyzed was body size. The author predicted that an animal with a large body would have more dexterity. This turned out not to be true, for many of the same reasons as stated above. But also, body size is dependent on many different factors (diet, habitat, phylogeny) and a small animal is just as likely to develop dexterity on the basis of these as a large animal.

Phylogeny was next on the list. It turned out to be correlated strongly with dexterity. Phylogeny refers to the evolutionary history of an animal and which other animals it is related to. The study found that more closely related animals tended to show more similar forelimb use patterns.

It was also predicted that those animals that lived in trees would be more dextrous. This was only related in terms of proximal dexterity. The author claimed that this is because grasping forepaws are not related to climbing trees.

Vertebrate predation is a factor that many claim gives rise to forelimb dexterity. But this study found that it was actually negatively correlated. This is possibly due to the fact that animals that prey on vertebrates also have to chase these animals down (the lion and the antelope, lynx and snow hares, polar bears and seals). Thus these animals forepaws must strike a balance between finally tuned dexterity and raw running power. The result is not always the most dextrous.

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Iwaniuk, Andrew N., 1997. "The Evolution of Skilled Forelimb Movements in Carnivoran." Masters Thesis, University of Lethbridge, Lethbridge. 151 p.  

Lions, Tigers, and Crocodiles

So the article for the week is about Crocodylian forelimb musculature. You may be asking yourself how that is related to iguanas, and well ... it's not really, other than it is yet another comparison. My interest of this article relates to its focus on why anybody is even studying Crocodylian forelimbs. The article, "Crocodylian Forelimb Musculature and its Relevance to Archosauria," discusses the forelimb of archosaurs as a functionally diverse anatomical unit, but one that has remained nearly the same through its evolutionary path (Meers, 2003).

Archosaurs are a group of creatures that evolved in the late Permian or early Triassic period. They are diapsid amniotes (meaning they have two holes in their skull, one on each side) and the most modern representatives are crocodiles and birds. This gives you a clue as to why their forelimbs are so interesting. The front limbs of an alligator (arms) vary quite significantly from the front limbs of birds (wings). But though they may look different, their musculature isn't all that distinct.

The author dissected 4 Alligator mississippiensis, 1 Crocodylus siamensis, 2 Crocodylus acutus, 2 Osteolaemus tetraspis, and 1 Gavialis gangeticus. They then compiled in depth muscle descriptions for all of the muscles in the forelimbs of the specimens. The muscles don't vary all that much from the iguanas. A part of this is because crocodylians are squamates, like iguanas, and hence their posture is very similar as are the muscles required to maintain this posture. The species dissected did have more extrinsic muscles on the ventral side. This means that they had more chest muscles (extrinsic meaning the muscles originate on the trunk and insert on the front limbs, and ventral being the side with the animal’s heart.) Also, the study named the deep muscles of the back differently than my sources did, but they were relatively the same.

The conclusion of the study was basically that the American alligator is representative of most Crocodylian species (re-enforcing that the forelimb musculature of Archosaurs has not changed much).

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Meer, Mason. "Crocodylian Forelimb Musculature and its Relevance to Archosauria." The Anatomical Records Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology (2003) 274A.2: 891-916. Web. 28 Apr 2012.

Updates

Okay, here are the updates for the week. I've finished both iguanas, photographed them completely, and I'm now on to completing my findings for the project. As I have explained before, this involves drawing comparisons between the iguanas, pigs, and cats. Obviously these are all quadrupeds, and therefore their muscles have a certain amount of similarities, but they are all different animals. Iguanas have a sprawling posture, their legs and arms extending beyond their bodies. Pigs are ungulates; the muscles are focused on keeping their bodies supported and allowing them to move forward and backward, in a single plane. Cats are carnivores, and hence their forelimbs are involved in prey capture and require a more specialized form. 

Hopefully within the next week I will be dissecting and photographing a fetal pig, which will allow me to show direct muscle comparisons between the iguanas and the pig, including a weight difference analysis as well as how their muscles differ with response to locomotion. 

I'm working on the first slides of the slide show right now, detailing the objective (which has changed several times), and the materials and methods. I'm also going through sources looking for information I can use for comparison. This is enormously frustrating because whenever you do a lit search, you seem to never find exactly what you want. I would like to find studies that are similar to what I've done -- a dissection, followed by detailed muscle descriptions, weights, and a locomotion analysis. Unfortunately, I haven't yet stumbled upon the perfect article, so I am just pulling bits and pieces from everything. 

Really?

So this week was pretty productive. I finished dissecting, photographing, and everything else - ing on Tuesday. It's pretty exciting to be done with both specimens. For the rest of the week I worked on putting together my presentation, which right now means analyzing data. Because of how my project has changed, "data analysis" is basically taking the muscle data I have for the iguanas and comparing it to other animals, particularly cats and pigs. These two were chosen because there has been so much research done on them, information is abundant. All three of the animals also have different habitats, and differing forms of locomotion. 

At the lab meeting this week, we read a pretty cool animal about extinct porcupines. Did you know that they can climb trees, along with goats and grey foxes? Well they can, and it is presumed that their ancestors could as well, this being deducted from their fossils. This may perhaps be quite a leap though. Today when we look at a species, we analyze their behavior, relate this to their musculature and then connect this with their bones. With fossils, this processed is reversed. Bones are looked at for robustness, bony landmarks, relative length and composition as well as muscle scars and attachments. These things are used to determine where muscles were and their possible actions, and this is then used to determine locomotion, environment, as well as the phylogeny of its descendants and ancestors. But it's certainly not an exact science, and sometimes things seem just a little far fetched.

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Opposites Attract

The study for this week looked at the distal forelimb musculature of the genus of lizards Liolaemus, which includes a particular species of sand lizard Liolaemus wiegmannii (Abdala and Moro 2006). I thought it would be interesting to compare their analysis with my own of the iguana considering their two very different forms of locomotion -- digging and walking in the sand vs. climb trees and swimming. The study went through all of the muscles in what we would call the forearm -- extensor carpi radialis, extensor digitorum, extensor carpi ulnaris, flexor carpi ulnaris, flexor digitorum (palmaris longus), flexor carpi radialis, as well as the muscles of the manus, which I did not analyze in the iguana. 

The article went through and wrote up muscle descriptions similar to how I wrote up muscle descriptions, commenting on the origin, insertion, and any other features of note. As I went through, I noticed there were slight differences between the two species, but nothing of particular note. I found this a little odd, considering the differences between iguanas and sand lizards, until I got to the conclusion of the article. It basically said that the general morphology of the forelimbs in lizards remains consistent across species. That because the set up is so general, it is easily used for many different forms of locomotion, and nothing is required to specialize over much. This is interesting because often times people study the specialization of species, why their musculature is different from everyone else and why this matters. But in this case, it's really the opposite. 


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Abdala, Virginia and Silvia Moro. "Comparative Myology of the Forelimb of Liolaemus Sand Lizards (Liolaemidae)." Acta Zoologica(2006) 87.1: 1-12. Web. 19 Apr 2012. 

Time Will Tell

Alright, this week in the lab, I started Iguana 2. As expected, it was very similar to the first iguana except for the fact that it was much smaller. This is a little ... off putting. Things don't look much different, but they are much smaller and this makes things slightly more difficult to find. The muscles thus far have weighed about half as much as the first iguana, which makes sense as the lizard is about half as big. Overall, not much to say. 

I'd also like to brief everyone on the changes to my project. Due to the time it took to dissect the first iguana as well as the shortness of time in general, the goals of the project have been modified. As you may have guessed, I am no longer working with anoles at all, as my original proposal suggested. The anoles are significantly smaller than the iguanas and it was easier for me to begin on a larger animal. Though I did have dissection experience prior to this project, I have never done something this in depth and hence was a little unprepared. I will also not be comparing the iguanas to any other lizards. Time just became too short, and it was only practical to dissect two lizards. I will instead be comparing the iguanas to mammals that are well documented - pigs and cats mainly. Lizard musculature differs from these mammals due to their habitat (trees and beaches), their posture (sprawling), and the fact that they are not mammals. I think it's a pretty cool comparison. 

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Means vs. Ends

Alright, the article for this week covers two subjects. The first is, you guessed it, iguanas. Specifically, general iguana ecology (was that an oxymoron?). It covers temperature preference, nesting and feeding habits. The second issue is an ethical one. 

Iguana body temperatures ranged from 34.0 degrees to 37.2 degrees Celsius (Hirth, 1963). This is 93.2 degrees to 98.96 degrees Fahrenheit, which is surprisingly not that far from human body temperatures. The air that they tended to reside in was 28 degrees C (82.4 F) to 32 C (89.6 F). Larger iguanas tended to rest in trees, while younger and smaller iguanas rested on the beach and none of the iguanas were ever far from the river or some other source of water. The scientists in the study believed this all had to do with thermoregulation. The water was a quick way for iguanas to cool down while the tree canopy offered heavy insulation, preventing loss of body heat. Remember that iguanas are cold blooded and hence cannot regulate their body temperature thus many of their adaptive behavior relates to thermoregulation.

Iguanas are herbivores, as mentioned before, surviving mainly on leaves and fruits. It has been found that young iguanas may feed on insects, however. As far as nesting goes, iguanas lay eggs in early spring, the most arid part of the year. The eggs are laid on the beach in spots that it takes the female iguanas some time to find. The scientists were not clear on what exactly the female iguanas were looking for, only that they searched for a significant amount of time to find a nesting site. 

As cool as all this iguana stuff is, the most interesting part of the article for me was the techniques used. In order to determine the body temperatures of the iguanas, the lizards were shot with .22 caliber rifle and then their temperature as well as the temperature of the surrounding area was taken as soon as possible. This seems a little ... out of line to me. The study was published in 1963, a time during which animal cruelty standards may have been different, but I'm not sure whether what was gained justified the shootings. Food for thought. 

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Hirth, Harold F. "Some Aspects of the Natural History of Iguana iguana on a Tropical Strand." Ecology (1963) 44.3: 613-615. Web. 11 Mar 2012.

Darwin Strikes Again

Integrative organismal biology (IOB). Not a term you hear everyday, but it refers to a part of biology that focuses on the ecology, behavior, and evolution of organisms. My paper for today is about the IOB of marine iguanas, a species closely related to the green iguanas I am working on (Wikelski and Romero, 2003). The study used a method of predicting evolution as the basis for its work. The idea is that if you study the performance of specific organisms you can determine which factors play a role in the selective process of evolution and then use these factors to predict how the species will evolve in the future. 

This study, "Body Size, Performance and Fitness in Galapagos Marine Iguanas," used foraging and reproductive performance as the factors to predict evolution. The reason marine iguanas were chosen as the model is because the body mass of iguanas on different islands can vary by one order of magnitude, adult iguanas really have no predators, and they don't compete with other vertebrates for food (iguanas eat the red and green algae revealed at low tide). This means that there is a ... regulated form of evolution occurring. The changes taking place are based on the iguanas alone, not on other species. 

The study found that larger marine iguanas, male or female, had better reproductive success. The females because they could produce larger babies which were more likely to survive and the males because they were able to control a larger territory and put on a better show for thefemales. However, being large comes with draw backs. The larger iguanas had far less foraging success. They had to expend more energy to move their larger masses, it takes more energy to heat a larger body (the whole cold blooded issue), and in the end, they had trouble getting enough food. When times were good, and algae abundant, the larger lizards did fine. However, when times were bad, like after a hurricane, it was the big lizards that died. 

The conclusion that was drawn from this data is that marine iguanas will continue to get bigger. Not only does reproductive success increase, but the world is getting warmer and that's good for the cold blooded species. However, their size will be regulated by the lack of foraging success. Bigger lizards need more food and sometimes it's just not there. Don't expect any giant iguanas anytime soon. 

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Wikelski, Martin and L. Micahael Romero. "Body Size, Performance and Fitness in Galapagos Marine Iguanas." Integrative and Comparative Biology(2003) 43.3: 376-386. Web. 4 Apr 2012. 

Uncertainty

I'm done with Iguana 1! The forelimbs of my first iguana have been completely de-muscled and now ... well they're just kind of bone that is barely attached to anything. I finally removed all of the deep muscles - the pronator teres, supinator manus, teres major, subscapularis, and the others. It was surprising that while some of the deep muscles were quite small, the majority of them were actually larger than the superficial muscles. For example, the teres major, which is a deep muscle of the back (one of the many that originates from the scapula) weighed significantly more than the trapezius and latissimus dorsi (both superficial muscles). With regards to the brachialis/brachioradialis issue I decided that there was only one muscle there and the muscle had been named differently by the different sources. The muscle itself seems to be more similar to the human brachioradialis as it has its insertion point on the radial shaft. It may be a fusion of the two muscles. 
 
Anyway, I can now start on my second iguana. The process for this one will be the same as the first, but I believe it will go much faster due to the experience I gained with the first. Skinning will hopefully only take one day, and then there is superficial identifications and separations, pictures, and then muscle removal. I already have my muscle catalogue complete, so with the second iguana I have to check with the catalogue and ensure that they agree. If they don't, I have to make a note and take further pictures of the area even though the specimen will have already been photographed. There can actually be quite a bit of difference between different samples of the same species. It is important to remember that bodies are adaptive and everything an animal does, eats, hears, sees, etc change its body chemistry and set up. There is a muscle in the human leg that 8% of humans don't have. Don't you just love the uncertainty?
 
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It's All ... Lizard to Me?

This week in the lab was ... not as productive as hoped. On Tuesday, I got a lot done. All the of the superficial muscles on my iguana were removed and weighed, revealing the deeper muscles below. Taking the muscles off was pretty simple. The hardest part was ensuring that the cut was made as close to the bone as possible. Because I am weighing the muscles for comparative purposes, it it important for the entire muscle to come off, and not just part. This was difficult because I was not familiar with the iguana skeleton. First of all, their clavicles extend all the way around their necks like a collar and they have a second interclavicle below acting like the clavicle in humans. Their sternum, instead of being a single line of bone as in humans, is almost a breastplate covering most of the chest. Some of the muscles that must be removed are attached underneath these bones, so it takes some maneuvering to get them out. 

Friday was an off day. I ended up getting sick and leaving early which means I missed out on almost an entire day of work. So next week I have to catch up and remove the deep muscles of the iguana. There really aren't that many, the problem is identifying them. For example, according to my iguana atlas (Oldham et al, 1975), iguanas have a brachialis muscle, but no brachioradialis. However, this source has been weak in identifying deep muscles. Another source on the forelimb muscles of monitor lizards (a species similar to iguanas), claims that there is only a brachioradialis and not a brachialis (Haines, 1939). However, this brachioradialis inserts and originates at almost the same place as the brachialis of the first source. Then there is the veterinary textbook I've been using (Dyce, 2002) that only references a brachialis muscle. But it uses the forelimb of carnivores for this, and iguana are not carnivores. And then there is the iguana itself. There appears to be only one muscle at the juncture of the elbow between the humerus and radius. There are several possible explanations for this. The first being that all the sources are speaking of the same muscle and have just named them differently. The second is that there are two muscles, but the sources all had different focuses and didn't mention them both. The third would be that there is a conflict in the scientific community about this particular muscle and no one really knows if there is one muscle, two muscles, a fused muscle, or some other variation. Welcome to the academic world.



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Dyce, KM, et al. Textbook of Veterinary Anatomy. St. Louis: Saunders, 2002. Print.

Oldham, Jonathan Clark and Hobart Muir Smith. Laboratory Anatomy of the Iguana. Dubuque: WC Brown,   1975. Print.

Haines, R. Wheeler. "A Revision of the Extensor Muscles of the Forearm in Tetrapods." Journal of Anatomy (1939) 73.2: 211-233. Web. 29 Mar 2012.

Deep

     Todays blog is on deep muscles. These are the muscles that ... well no one really talks about. Everyone knows about the biceps and triceps, pectorals and deltoids, but not many people discuss the teres major or the pronator quadratus. My iguana has been almost completely de-muscled except for these deep muscles, and to be honest, I'm not really sure what to be looking for. So Dr. Zack helped me out with two papers on the homologies of tetrapod forearm extensors and flexors. 

     The first paper (Haines, 1939) details the results of a study that compares the forearm extensor musculature of Chelonia (turtle), Sphenodon (lizard), Salamandra (salamander), Ophiacodon (synapsid), the giant salamander, Eryops (early amphibian), Rana (frog), Varanus (monitor lizard), crocodilians (this seems obvious), monotremes (mammals that lay eggs), and Didelphys virginiana (opposum). It was a pretty extensive study. What I took away from it, is that generally species living in similar environments have similar muscles, which makes sense given that they have to do similar things. Evolution is consistent like that especially because this study was focusing specifically on homologies (something that is shared in present species because it was shared by a common ancestor). I also determined that in my iguana I need to be on the look out for brachioradialis, which allows for the rotation of the forearm, supinator manus, which allows for the supination of the hand, and supinator manus accessorius, which helps in the supination of the hand. I believe I have already found the brachioradialis, but the other two I haven't looked for yet.
     The second paper was slightly less in depth (Haines, 1950). It compared many of the same species as the previous study, but really focused on Varanus (monitor lizards) and Felis (cats). The main take away for me was that I need to be looking for pronator profundus, which in humans is often called pronator teres and allows for the pronation of the hand, and pronator quadratus, which does the same. Keep in mind, the forelimb of my iguana is only maybe three inches in length, and on humans these muscles are only maybe an inch or two long. They're tiny in iguanas. 
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Haines, R. Wheeler. "A Revision of the Extensor Muscles of the Forearm in Tetrapods." Journal of Anatomy (1939) 73.2: 211-233. Web. 29 Mar 2012. 

Haines, R. Wheeler. "The Flexor Muscles of the Forearm and Hand in Lizards and Mammals." Journal of Anatomy (1950) 84.1: 13-29. Web. 29 Mar 2012. 

King of the Jungle

Alright, another lit search turned up a pretty cool article. Though it is not directly related to iguanas, I think it offers some cool insights in to the musculature of the forelimb in a variety of species. The study was conducted to analyze the evolution of pectoral and forelimb muscles from bony fish to non-mammalian tetrapods and then further to monotreme and therian mammals, including humans.
Bony fish or sarcopterygians have very few muscles in their "upper bodies." They have a fin abductor and adductor and then some undifferentiated hypaxial and epaxial muscles. This makes sense when you consider that fish aren't doing a lot of heavy lifting. This also explains why there was a large change upon the evolution of tetrapods (creatures that walk on four legs). Species that walk must support half their weight on their forelimbs and their pectorals and back muscles have to support their entire body weight on their limbs. Many species have heavily developed shoulder and back muscles due to their large body mass. For example, hippos have a huge weight in their trunks and they have to move this when they walk. The muscles around the trunk have to not only stabilize this mass, but also move it against the force of gravity, mud, water, etc. That's a lot of requirements and is the reason that nature went from fish with 2 clear forelimbs muscles to over 40. And these forty muscles has not undergone a large amount of change since then, mainly because the same requirements are still present (Diogo, 2009).
All of the current forelimb muscles -- biceps, triceps, coracobrachialis, extensor carpi ulnaris, flexor carpi radialis, extensor digitorum, and about twenty others -- derived from the first two forelimb muscles in fish, the fin abductor and adductor. Oddly enough, the pectoral muscles developed from the "postcranial axial" muscles. These are the muscles that are below the head and towards the center of the body. I have to say, the whole article was very odd. It is not very often that I think about how I am descendant from fish. Does that strike anyone else as ironic? You know how we now eat fish and consider them fairly low on the food chain, it's very Lion King ;)
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Diogo, R., Abdala, V., Aziz, M. A., Lonergan, N. and Wood, B. A. “From Fish to Modern Humans – Comparative Anatomy, Homologies and Evolution of the Pectoral and Forelimb Musculature.” Journal of Anatomy (2009), 214.5: 694–716. Web. 23 Mar 2012.

When the Iguana Bites

     Okay, it's Spring Break this week, so I've been occupying my time with more lit searches. Todays piece is on ventilation in iguanas and the muscle involved in this. The study found that only four hypaxial muscles are involved in iguana breathing. (A hypaxial muscle is one located on the ventral trunk or the limbs i.e. the muscles of the abs, pecs, arms, and legs, but not those in the back.) The four muscles are the transversalis, the retrahentes costarum, and the external and internal intercostals. The first two are the muscles that control expiration, while the second two control inspiration, however, lizard respiration is a little different than normal (Carrier, 1989).     Iguanas bring air into their lungs by changing the shape of the thoracic cavity to create a sub-atmospheric pressure. If this sounds uncomfortable (the whole deforming of your body in order to breathe), it may be. Recent studies have shown that lizards cannot run and breathe at the same time. In most mammals, the more arduous the activity, the more oxygen we attempt to bring into our bodies, hence the panting that often accompanies running. But lizards can't do this. The author of this article, David Carrier, believes that this is caused by the opposing demands that the ventilatory and locomotive muscle place on the thorax. Both sets of muscles are pulling in different directions, thus reducing the effectiveness of both. Oddly enough, aspiration in iguanas begins with expiration followed immediately by inspiration, but this cycle is usually followed by a period of breath holding. Many humans do the same thing when they become aware of the sounds of their own breathing, particularly if they are standing close to someone else. It's odd how many of those parallels you find.
     So the transversalis and the retrahentes costarum are responsible for expiration. Pretty straight forward. In an iguana, the transversalis is located on the ventral side of the ribcage deep to the intercostals and obliques, while the retrahentes costarum is located on the dorsal side of the ribcage deep to the intercostals and obliques. When these muscle contract, they increase the pressure in the thoracic cavity and aid in the exhalation of the air in the lungs.
     The intercostals are responsible for inspiration, sort of. The internal intercostal lies superficial to the transversalis and the external intercostal lies superficial to the retrahentes costarum. When either of these muscles are stimulated ventrally, thoracic pressure is decreased. But if they are stimulated dorsally, thoracic pressure is increased. Thus these muscles are partially responsible for both parts of breathing.
     Also, these muscles are all composed of both slow twitch fibers and fast twitch fibers. Slow twitch fibers are what allow a marathoner to run 26.5 miles, or a weight lifter to hold a weight in the air for five minutes. They are the endurance fibers. The fast twitch fibers are the sprinters, the ones that produce a large boost of speed or power and then have to wait to be reactivated. The muscles that were responsible for respiration in iguanas relied mainly on slow twitch fibers to accomplish this. That means that there was a significant delay between the muscle activation (the thought to breathe) and the actual beginning of a breath.

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Carrier, David R. "Ventilatory Action of the Hypaxial Muscles of the Lizard Iguana Iguana: A Function of Slow Muscle." Journal of Experimental Biology (1989) 143: 435-457. Web. 22 Mar 2012. 

Another Day, Another Lizard

     So, this is what I did in the lab this week. Tuesday I continued with my muscle descriptions. My first draft, as usual, was a little scatter-brained and some of the terminology was not what it should have been. Anatomical terminology, which seemed so straight forward earlier this year in anatomy, has complicated infinitely. This is due mainly to the fact that I am no longer dealing only with humans. In humans, you use the terms posterior/anterior, medial/lateral, and superior/interior. However, in quadrupeds, which I'll point out is essentially most of the other creatures on the planet, you use dorsal/ventral, medial/lateral, and cranial/caudal. Originally, when I wrote my muscle descriptions I used a combination of both, which made everything unclear and un-standardized.
     For those of you who don't study biology in your spare time, dorsal and ventral basically mean back and front. In humans, this is very obvious; however, in other species, dorsal is the side of the animal where the backbone lies, and ventral is the side with the ribcage/heart. More like the top and bottom. Medial and lateral are how far away something is from the center of the body. Cranial and caudal refer to distance from the head. Cranial is obviously closer, and caudal is farther away. The terms distal and proximal are also used to describe the distance from the trunk when discussing structures in the limbs. I hope that cleared things up.
     So Tuesday, that is what I did. Today, I started to remove muscles. This seems simple, you just cut it off right? Wrong. To remove a muscle, you follow it to both the insertion and origin. Here you must cut the connecting tendons as close to the bone as possible to avoid losing data. After the muscle is removed, you weigh the muscle, record the weight, and then photograph everything again without that muscle. Then you move to the next one. It is a tedious, but necessary process.

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Night of the Living Iguana

     Okay, so I'm back to only two blogs a week. The first will be a summary of an article I have found in my research, and the second will be an overview of what I did (and didn't) accomplish in the lab. So here is my literature blog.
     So I found this article on the adaptations in the hind limb of lizards due to their sprawling posture (Rewcastle, 1983). There are technically two "problems" with their sprawling posture. The first being a problem of support. Because the body of the lizard does not sit directly above the limb supporting it, there is a lack of support for the body. Pull on your physics here, guys. The second problem occurs because the limb is so far from the body. The limb cannot rotate completely around without the bones in the hind limb, primarily the femur, running in to the hip or the edge of the acetabulum. In response to these constraints, lizards have evolved some special features. First, the femur of the lizard is abnormally long. In most quadruped mammals, the tibia and fibula are longer than the femur. In lizards, this is almost universally untrue. The femur is longer than the tibia and fibula, creating a longer moment arm for limb movement. However, this creates another problem, the longer moment arm makes the limb heavier and requires a significantly larger muscle mass to move it. The muscle I talked about in my prior post -- the caudofemoralis longus -- is one of the major muscles in the hindlimb, a muscle abundantly developed to move the hip.
     Another adaptation occurs in the ankle and foot. The tarsals of the foot/pes, have fused together, to create a more stable base, while the proximal metatarsals have grown to overlap one another and allow for the foot to be used as another lever. The pes also became more asymmetrical, with the first three digits elongating and falling on essentially the same plane, while the fourth and fifth digit became more autonomous. This development is believed to reflect an adaptation to arboreal/tree environments. The limb adaptations do require that the body of the lizard be significantly reduced in weight.
     This author also took the time to mention that the lizards sprawling stance does afford the lizards some advantages. First of all, it allows the body to lay closer to the substrate on which it's moving while still letting the limbs move. Think about it like this, if a lion were to lay nearly on its stomach on the ground and try to walk forward, it would fall on its face and look ridiculous. But if a lizard did that (and they do quite often, probably in your backyard), it would be able to move its limbs freely. The hindlimb apparatus allows for short bursts of incredible speed while keeping the lizard close to the ground and away from danger. This indicates a propensity in lizards to live in/on the ground or in the trees.

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Rewcastle, Stephen Compton. "Fundamental Adaptations in the Lacertilian Hind Limb: A    Partial Analysis of the Sprawling Limb Posture and Gait." Copeia (1983) 1983.2: 476-487. Web. 14 Mar 2012. 

If I Don't Tell You, You'll Have to Kill Me

     Another day in the lab, and there was tons to do today. Unfortunately, I didn't get as far on Tuesday as I would have liked, so Dr. Fisher and I were not able to start removing the forelimb muscles. I spent the morning writing up my dissection notes. As I skinned and separated the muscles of the forelimb, I took notes on the characteristics, origin, insertion, and any other observations regarding the muscle. The theme today was "document everything." My dissection notes, I found, as I typed them up, were lacking. Dissection notes look something like this: 
               Muscle Name: Latissimus Dorsi
               Muscle Origin: The muscle originates from the thoracodorsal fascia, located      around the spine at the mid back. The muscle originates via an aponeurosis (a thin, widespread layer of tendon). The muscle itself is thin and extends over most of the scapula and deep to the trapezius. It has only one belly. 
               Muscle Insertion: The muscle inserts on the proximal shaft of the humerus, attaching with a single tendon that is the thickest part of the muscle. 
               Notes: The latissimus dorsi was easy to separate from trapezius, however it was damaged during dissection on the edge that borders the shoulder. A single cut extends approximately 2 mm into the muscle mass. 
     Impressive, right? However, upon my first dissection, I noted almost none of this. Therefore, today required some back tracking. I went back and re-examined my muscles, rewrote my notes, and came out on top. Sort of. I am now a day behind, and the lab schedule must be revised. Oddly enough, Dr. Fisher was not surprised by this. 
     I spent the afternoon photographing the iguana in all its glory. I first took pictures of the iguana in every position I could think of, keeping a scale in the picture at all times. This required several tries, fixing lighting, focus, glare, etc. After getting this done, I went back and numbered all the muscles of the forelimb, re-photoing in all the same positions as before, fixing lighting, focus, glare, etc. It was exhaustive, but after a muscle is removed, any information it may have held is gone. Having photographs of everything lessens the chances that something will be missed. But, of course, no one is perfect. 

AA