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. 

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Dawn of the Dinosaurs

     Alright guys, it was another day of research - a literature search to be exact. The article for today is "Caudefemoral Musculature and the Evolution of Theropod Locomotion," by  Gatesy (1990). Theropods are bipedal dinosaurs, and they eventually gave rise to some avian species. However, the researchers used iguanas as a comparative group and went into a discussion of the evolution of the iguana femur and the muscles the allow the iguana to move, with particular emphasis on the importance of tails in locomotion. 
     In this study, Dr. Stephen Gatesy was attempting to show how the caudofemoralis longus muscle of the dinosaurs - which allowed them to retract their leg and hence act as the major impetus for locomotion - has shrunken in their modern day descendants as their tails have grown smaller or disappeared. For those non-anatomy people, caudofemoralis longus is a muscle in the thigh area of prehistoric dinosaurs that extends from the tail to the femur. Its name gives much of its identity. 'Femoralis' obviously indicating that it is near or attached to the femur, 'caudo' meaning tail of toward the tail, and 'longus' referring to relative size (longer) compared to the muscle caudofemoralis brevis. 
     Iguanas are not Theropods. They do not walk on two feet and are not directly descended from dinosaurs. But, like I said, they were used as a comparative group along with a Savannah monitor, a horned lizard, an American alligator, a spectacled caiman, a bobwhite quail, a domestic fowl, a helmeted guinea fowl, and a domestic pigeon as well as the bones of several dinosaurs. 

     The CFL (caudofemoralis longus) of the iguana was 17 - 36% of the dry muscle mass of the hind limb. This is quite large, considering the amount of muscles in the hind limb. The CFL originates from the caudal vertebrae in the proximal 1/3 of the tail. The term ‘proximal’ refers to the part of the tail closest to the body.  Though this may seem like a weird attachment point, as the muscle then inserts on the trochanteric fossa of the femur, keep in mind that an iguana's tail is almost 2/3 of the iguana's length. The trochanteric fossa is located on the proximal end of the femur, which is why this muscle acts as the major mover of the femur. Iguanas, like many other lizards, have a hind limb that sits fairly far away from the body, and during movement, the femur is retracted 140-165 degrees. Though this sounds very scientific, it is easy to imagine. Picture a lizard and how it walks. There is a large upward movement of the hind limb as it pushes itself forward, almost as if it has a hitch in its gait. If you can't see it, watch this video of Lung, the green iguana, walking. On a leash (http://www.youtube.com/watch?v=iSSWvS_5Rvc). Pay particular attention to the orientation of the hind limb and how it moves as Lung walks. Enjoy the dramatic music :) 
    

The CFL is muscle number 3. 

     The CFL may also be responsible for the retraction of the entire hindlimb, not just the femur. It may be responsible for the rotation of the hind limb, the fixation and flexion of the knee joint, and the lateral movement of the tail. Cool stuff. 

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Gatesy, Stephen. "Caudefemoral Musculature and the Evolution of Theropod Locomotion." Paleobiology (1990)      16.2: 170-186. Web. 8 Mar 2012. 

The Iguana Files: Part 1

     Third day in the lab! Today I started dissecting my first iguana specimen, aptly named "Iguana 1." I first skinned both forelimbs, the upper back and upper chest. This revealed all the muscles of the forelimb and their attachments throughout the back and chest. Skinning took longer than expected due to the weird position of the lizards arms. They were lying flat against its sides, making it hard to reach the skin laying against the body. It took some bizarre maneuvers of the scalpel and the help of gravity, but eventually I got all the outer layer off. However, I ended up damaging the flexor carpi ulnaris of the left forelimb. This is the muscle on the forearm that allows the wrist to bend on the thumb side. 
     After the skin came off, I had to separate the muscles of both limbs. There are several ways of doing this. The first is called the "scissor method," which requires sticking a pair of scissors between two muscles and gentling opening them to pull them apart. This allows the dissector to feel if there is a large resistance, which would indicate that the two muscles you thought you saw were, indeed, one muscle. Another method is using a scalpel and a pair of tweezers to slowly cut the muscles apart. This method allows for a lot more mistakes because a scalpel will cut through almost anything, easily. The last is using a dull probe to push along the boundaries between two muscles and separate them. I used all three with my lizard today. 

This is one of the sources I'm using to identify the muscles of the forelimbs. There are a lot more than are shown though. :(

     I then began photographing the limbs. I placed numbers on those muscles that I identified. These numbers corresponded to a list of muscles in the forelimb, which obviously allows me to easily identify the muscles in the pictures. I also photographed the limbs without numbers, for more reference. On Friday, Dr. Fisher and I will begin removing the superficial muscles of the forelimb to reveal the deep ones and eventually the bone and muscle attachment points. That's all for now. 

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Pregnant and Wicked Fast

This is a wallaby. Well, two actually. 

     Alright, so Friday was my second day in the lab and I split my time between dissection and research. In the morning I spent time with my clawed friend, finishing skinning his left hindlimb and separating the muscles on all four limbs. I then used my handy dandy lab binder to start identifying the muscles in the limbs. It's rather bizarre when you look at something on an animal far unrelated to you, and notice how similar everything is. The major differences I noted were that many of the muscles in the thigh were oriented differently and there were some I had never seen before. Also, because the lizard was heavily preserved, it was sometimes hard to tell if a section of muscle was in fact more than one muscle, or all the same. For those of you who have never dissected, muscle appears similar to ... well, fish actually. You know when you cut into a piece of raw or uncooked fish and it all sort of flakes away? Those are fish muscles-and iguana muscles behave similarly under a scalpel. I had to rely heavily on the diagrams to determine where to cut and separate. 

     I spent the rest of the day taking advantage of ASU's massive online library, searching for more papers on iguana ecology, morphology, and anatomy. Literature searches are often frustrating to me because I know in my head exactly what I want, but it is usually not what I find. Compromise isn't my favorite word, so I tend to wade through massive amounts of sources searching for the perfect one, only to reach the end with nothing. But today I found two sources that I really liked. The first was on pregnant or gravid iguanas and how they are capable of increasing their acceleration even while carrying the extra mass of their clutch of eggs. This was made possible with more force produced by the muscle as well as a longer length of time the foot was left on the ground. The scientists actually theorized that female iguanas who were not pregnant did not have enough mass to fully "load" their muscles and hence were not reaching their potential (Scales, 2007). 

     The second source was regarding the amount of stress the bones in the iguanas hindlimbs underwent due to their more sprawling orientation. Iguanas have higher limb bone safety factors than most mammals. A limb bone safety factor demonstrates how much extra force a bone can take beyond normal. For a bending motion, iguanas have a limb bone safety factor of 5.5 - 10.8. This means that a lizard bone can receive up to 10 times more force than it normally receives. This is abnormally high and unnecessary. This may indicate an evolutionary drawback (Blob, 1999). 

     An afternoon of research was lightened when Dr. Fisher took out some specimens from the freezer.  Today, the wallaby came out of the freezer and moved to the fridge to thaw. It was a little wrapped up in itself, with its tail wrapped around it's body. We also saw the ringtail and it, according to Dr. Fisher, was "cute" and "soft." Personally, I thought it looked a little feral, but in a lovable, endearing way :) We had lab meeting at four and discussed some articles written by Dr. Fisher and her colleagues on red pandas and pygmy hippos.  Did you know hippos have four fingers, not hooves like horses and cows? I didn't either. 

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Scales, Jeffrey and Marguerite Butler. "Are powerful females powerful enough? Acceleration in gravid green                iguanas (Iguana iguana)." Integrative and Comparative Biology (2007) 47.2: 285-294. Web. 2 Mar 2012.

Blob, Richard W. and Andrew A. Biewener. "In Vivo Locomotor Strain In The Hindlimb Bones Of Alligator Mississippiensis And Iguana Iguana: Implications For The Evolution Of Limb Bone Safety Factor And Non-Sprawling Limb Posture." The Journal of Experimental Biology (1999) 202.9: 1023-1046. Web. 2 Mar 2012. 

It's a Long Way Down

     Alright, so these last two days I've split my time between creating a "lab binder" and researching the ecology and locomotion of green iguanas. A lab binder is basically a binder filled with any information one may need while dissecting - diagrams of limbs with corresponding muscle locations and names, dissection techniques, origin and insertion point sheets for different muscles, etc. So far, I have several diagrams of lizard forelimbs and hindlimbs showing the muscles both superficially and deep. I also have several listings of all the different muscles I should find with their origins, insertions, and actions (abductor, adductor, flexor, extensor, etc.). Dr. Fisher also sent me a PDF file detailing exactly how to go about dissecting the iguana. Where to start the first cut, which direction to go, how to go about skinning the fingers and toes. That is also in there.
     My research of iguanas has turned up this so far: First off, iguana anatomy is not so different from, say, pig anatomy. They have essentially the same bones - the humerus, radius, and ulna in the forelimb; the tibia, fibula, and femur in the hindlimb; a spinal cord and a skull. Iguanas also have five fingers and toes, just like humans do. The only major difference is the orientation of the bones. Because lizards are quadrupeds, their forelimbs and hindlimbs serve different purposes than in bipeds. The muscles that move these limbs are also different. Some are bigger than those in humans, some are completely foreign, and some you are expecting but do not find.
     Green iguanas (Iguana iguana), are, as the name suggests, bright green. They often have dark stripes around their tails and spines up their backs (Lagasse, 2011). They are strictly herbivores, though some iguanas that migrated to Florida have begun eating snails (Townsend et al., 2005). They grow to be 3-6 ft long, 2/3 of that length being their tail (Lagasse, 2011), which will grow back if taken off by a predator (Stewart, 2004).
     Green iguanas live in tropical areas from Mexico to Southern Brazil. They dwell primarily around rivers where there is abundant foliage. These lizards are arboreal - they live in trees - which is partially why their digits are tipped with claws, to aid in climbing. They are also accomplished swimmers, able to stay under water for close to 40 minutes in a lethargic state. Their large tails aid in propulsion in the water. Often when threatened, iguanas will jump from the trees into the water, their hard scales able to protect them from a 50 ft drop (Stewart, 2004).                                                
     I also found some interesting behavioral characteristics of iguanas. Many juvenile iguanas live and sleep in groups not only for warmth but also for protection from predators. Scientists have found that iguanas that live in groups tend to grow faster than those alone. The lizards also tend to protect their siblings, with identification possibly deriving from scent. The brothers will often put themselves in front of their sisters, the reasoning supposedly being that inherited traits will more likely be passed down through females than males (Stewart, 2004).
     I don't know, iguanas are kind of cool. Though beware, there were also a bunch of articles about how iguanas carry a bunch of diseases and often infect infants if they are kept as pets. They are also eaten. Yum :)

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                                                        Works Cited

Lagasse, Paul. “Iguana.” Columbia Electronic    Encyclopedia, 6th Edition (2011): 1. MasterFILE Premier.    Web. 1 Mar 2012.

Stewart, Doug. “Friendly Dragon.” National Wildlife 42.5 (2004): 38R. MasterFILE Premier. Web. 1 Mar 2012.

Townsend, Josiah H., et al. “Predation of a Tree Snail Drymaeus multilineatus (Gastropoda: Bulimulidae) by Iguana iguana (Reptilia: Iguanidae) on Key Biscayne, Florida.” Southeastern Naturalist 4.2 (2005): 361-364.JSTOR. Web. 1 Mar 2012.