What do they compare the scales on the back of a croc to?

Epidermal body armour and skeleton of a black caiman (Melanosuchus niger).

Crocodile armor consists of the protective dermal and epidermal components of the integumentary system in animals of the social club Crocodilia.

Structure and anatomy [edit]

The epidermal exoskeleton of the alligator consists of oblong horny scales, arranged in transverse rows; the long axes of the scales are parallel to that of the body. On the tail, except along the mid-dorsal line, and on the ventral side of the body and caput these scales are very regular in outline and system; on the sides of the head and torso and on the legs they are much smaller and less regularly arranged, while along the mid-dorsal line of the tail, especially in its posterior half, they are elevated into tall keels that requite the tail a large surface surface area for swimming. The starting time three digits of both mitt (fore foot) and pes (hind human foot) are armed with horny claws, which also belong to the epidermal function of the exoskeleton.

The dermal exoskeleton consists of bony scutes that underlie the epidermal scales of the dorsal surface of the trunk and anterior part of the tail. The overlying scales, except in very young animals, are always rubbed off, so that the bony scales are exposed. The ventral or inner surface of the scutes is flat, while the outer surface is strongly keeled and in old animals is frequently crude and pitted. The plates are nearly square in outline and are closely joined together in most places.

The scutes are grouped in two fairly distinct areas known as the nuchal and the dorsal shields. The quondam lies only back of the head, in the region of the fore legs, and consists of iv larger and a number of smaller plates. The latter, or dorsal shield, extends over the back in fairly regular longitudinal rows and quite regular transverse rows. At the widest part of the trunk there are half-dozen or 8 of these scutes in one transverse row. They get smaller towards the tail.

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 peel. One pair, each of which may be as large as a walnut, is establish on the lower side of the caput, ane on the inside of each half of the mandible. The other pair is within of the lips of the cloaca.

Histology of the integument [edit]

The epidermis of an embryo, young, or half-grown Crocodilia contains the rete Malpighii: a unmarried layer of short, cylindrical cells. Over the rete are somewhat flattened, disk-shaped cells formed by transverse partition of the underlying rete cells. On the outside lies the epitrichial layer, a mosaic of polygonal cells each with an oval nucleus almost its middle. Between the epitrichial cells are small oval holes, not unlike the stomata in the epidermis of plant tissues. Bronn^[2] thinks these are not artifacts, but he does not suggest any explanation of their occurrence.

On the curt, cylindrical rete Malpighii cells are flattened cells that gradually become very flat and lose their nuclei as they laissez passer 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 unremarkably be adamant by the groups of pigment granules. On the cells of the more than superficial layers of the stratum corneum are direct, dark lines, maybe ridges caused by pressure level of the over- or underlying polygonal cells. The individual cells of the horny layer are normally easily isolated in the abdomen 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 sure, though he thinks they probably are.

Rathke^[3] pointed out that on the surface of sure folds of the integument, particularly in the region of the jaws, are found in all Crocodilia sure small-scale, scattered, wart-similar 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 vivid, round cells that are closely united, without visible intercellular substance. Handling with potassium hydroxide and then with water will show sometimes, though not ever, fine granular nuclei in the cells. In probably all members of the genus Crocodilus, at to the lowest degree is plant, on the thick swelling on the right and on the left side of the cervix and trunk, a pocket-sized, flat pit which has the advent of the opening of an integumental gland. The pits are present also in the scales of the pharynx, nether 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 plant in the gavials just are absent-minded in some, probably all, alligators. A minor knob projects from the eye of some of the pits. These pits are non openings of glands but have virtually the same construction equally the pits seen in the head.

The integumental basic in the Crocodilia originate in the connective tissue of the cutis. Investigations in young animals show that these basic normally accept their origin in the under and middle layers of the cutis and generally work towards the periphery.

Footnotes [edit]

1. ^ Gadow 1923.
2. ^ Bronn 1859.
3. ^ Rathke 1866.

Sources [edit]

• 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 published Knickerbocker Press, 1915; electronic reprint c2000 Arment Biological Press.

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Source: https://en.wikipedia.org/wiki/Crocodilian_armor

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