Crocodilian armor
Crocodile .
Structure and anatomy
The epidermal
The dermal
The scutes are grouped in two fairly distinct areas known as the
The teeth are exoskeletal structures, partly of ectodermal, partly of dermal origin. They are conical in shape, without roots, and are replaced when lost. They will be described in connection with the skull.
Musk glands, said by Gadow[1] to be present in all Crocodilia, are found in both sexes and are derivations of the skin. One pair, each of which may be as large as a walnut, is found on the lower side of the head, one on the inside of each half of the mandible. The other pair is inside of the lips of the cloaca.
Histology of the integument
The epidermis of an
On the short, cylindrical rete Malpighii cells are flattened cells that gradually become very flat and lose their nuclei as they pass over into the horny layer. The stratum corneum consists of strongly flattened cells in which the nuclei can no longer be clearly seen, though their location can usually be determined by the groups of pigment granules. On the cells of the more superficial layers of the stratum corneum are straight, dark lines, perhaps ridges caused by pressure of the over- or underlying polygonal cells. The individual cells of the horny layer are usually easily isolated in the belly and neck regions where they never become very thick; but in the back the cells in this layer are very numerous and fuse with each other to form the bony plates; here the rete is the only clearly differentiated layer. Whether prickle cells are present in the epidermis of the crocodile Bronn is not certain, though he thinks they probably are.
Rathke[3] pointed out that on the surface of certain folds of the integument, especially in the region of the jaws, are found in all Crocodilia certain small, scattered, wart-like elevations, around each of which is customarily a narrow, shallow, circular groove; they usually have a dark brown but sometimes a gray or even white color. Microscopic examination shows these warts to be of epidermal origin, consisting of bright, round cells that are closely united, without visible intercellular substance. Treatment with potassium hydroxide and then with water will show sometimes, though not always, fine granular nuclei in the cells. In probably all members of the genus Crocodilus, at least is found, on the thick swelling on the right and on the left side of the neck and trunk, a small, flat pit which has the appearance of the opening of an integumental gland. The pits are present also in the scales of the throat, under the side of the neck, sides of the body, lateral and ventral surfaces of the anterior half of the tail, and the legs. They are near the hinder border of the scales. Only occasionally are two pits found in one scale. These pits are found in the
The integumental bones in the Crocodilia originate in the connective tissue of the cutis. Investigations in young animals show that these bones usually take their origin in the under and middle layers of the cutis and generally work towards 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) Archived 2005-11-24 at the Wayback Machine. Originally published Knickerbocker Press, 1915; electronic reprint c2000 Arment Biological Press.