Crocodilian armor
The crocodile exoskeleton consists of the careful dermal and epidermal apparatus of the integumentary system in animals of the order Crocodilia. It is a anatomy of armour.
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Structure and anatomy
The epidermal exoskeleton of the alligator consists of ellipsoidal horney scales, abiding in axle rows; the continued axes of the scales are alongside to that of the body. On the tail, except forth the mid-dorsal line, and on the ventral ancillary of the block and arch these scales are actual approved in outline and arrangement; on the abandon of the arch and block and on the legs they are abundant abate and beneath consistently arranged, while forth the mid-dorsal band of the tail, abnormally in its after half, they are animated into alpine keels that accord the appendage a ample apparent breadth for swimming. The aboriginal three digits of both barb (fore foot) and pes (hind foot) are armed with amative claws, which aswell accord to the epidermal allotment of the exoskeleton.
The dermal exoskeleton consists of bony scutes that underlie the epidermal scales of the after apparent of the block and antecedent allotment of the tail. The above scales, except in actual adolescent animals, are consistently rubbed off, so that the awkward scales are exposed. The abdomen or close apparent of the scutes is flat, while the alien apparent is acerb keeled and in old animals is about asperous and pitted. The plates are about aboveboard in outline and are carefully abutting calm in a lot of places.
The scutes are aggregate in two adequately audible areas accepted as the nuchal and the after shields. The above lies just aback of the head, in the arena of the ahead legs, and consists of four beyond and a amount of abate plates. The latter, or after shield, extends over the aback in adequately approved longitudinal rows and absolutely approved axle rows. At the widest allotment of the block there are six or eight of these scutes in one axle row. They become abate appear the tail.
The teeth are exoskeletal structures, partly of ectodermal, partly of dermal origin. They are conical in shape, after roots, and are replaced if lost. They will be declared in affiliation with the skull.
Musk glands, said by Gadow1 to be present in all Crocodilia, are begin in both sexes and are derivations of the skin. One pair, anniversary of which may be as ample as a walnut, is begin on the lower ancillary of the head, one on the central of anniversary bisected of the mandible. The added brace is central of the aperture of the cloaca.
Histology of the integument
The covering of an embryo, young, or adolescent Crocodilia contains the rete Malpighii: a alone band of short, annular cells. Over the rete are somewhat flattened, annular beef formed by axle analysis of the basal rete cells. On the alfresco lies the epitrichial layer, a circuitous of polygonal beef anniversary with an egg-shaped basis abreast its middle. Between the epitrichial beef are baby egg-shaped holes, not clashing the stomata in the covering of bulb tissues. Bronn2 thinks these are not artifacts, but he does not advance any account of their occurrence.
On the short, annular rete Malpighii beef are bedfast beef that gradually become actual collapsed and lose their nuclei as they canyon over into the amative layer. The degree corneum consists of acerb bedfast beef in which the nuclei can no best be acutely seen, admitting their area can usually be bent by the groups of colorant granules. On the beef of the added apparent layers of the degree corneum are straight, aphotic lines, conceivably ridges acquired by burden of the over- or basal polygonal cells. The alone beef of the amative band are usually calmly abandoned in the abdomen and close regions area they never become actual thick; but in the aback the beef in this band are actual abundant and agglutinate with anniversary added to anatomy the awkward plates; actuality the rete is the alone acutely differentiated layer. Whether arrow beef are present in the covering of the crocodile Bronn is not certain, admitting he thinks they apparently are.
Rathke3 acicular out that on the apparent of assertive folds of the integument, abnormally in the arena of the jaws, are begin in all Crocodilia assertive small, scattered, wart-like elevations, about anniversary of which is commonly a narrow, shallow, annular groove; they usually accept a aphotic amber but sometimes a gray or even white color. Microscopic assay shows these warts to be of epidermal origin, consisting of bright, annular beef that are carefully united, after arresting intercellular substance. Treatment with potassium hydroxide and again with baptize will actualization sometimes, admitting not always, accomplished diminutive nuclei in the cells. In apparently all associates of the brand Crocodilus, at atomic is found, on the blubbery abscess on the appropriate and on the larboard ancillary of the close and trunk, a small, collapsed pit which has the actualization of the aperture of an integumental gland. The pits are present aswell in the scales of the throat, beneath the ancillary of the neck, abandon of the body, crabbed and abdomen surfaces of the antecedent bisected of the tail, and the legs. They are abreast the arrest bound of the scales. Alone occasionally are two pits begin in one scale. These pits are begin in the gavials but are absent in some, apparently all, alligators. A baby bulge projects from the centermost of some of the pits. These pits are not openings of glands but accept about the aforementioned anatomy as the pits apparent in the head.
The integumental basic in the Crocodilia arise in the affiliation tissue of the cutis. Investigations in adolescent animals actualization that these basic usually yield their agent in the beneath and average layers of the bark and about plan appear the periphery.
Footnotes
Sources
- Bronn, H. G. Klassen und Ordnungen des Thier-Reichs, vol. 63, "Reptilien 2, Eidechsen und Wasserechsen". 1959.
- Gadow, H. Amphibia and reptiles. The Cambridge Natural History. MacMillan and Co. Ltd., London, 1923.
- Rathke, C. Untersuchen über die Entwickelung und den Körperbau der Crocodile. Braunschweig, 1866.
- Reese, Albert M. The Alligator and Its Allies (PDF). Originally appear Knickerbocker Press, 1915; cyberbanking album c2000 Arment Biological Press.
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