The Integumentary System 85 



scales of the fish, these scales are not separable. They are of epi- 

 dermal origin, actually being thickened portions of the stratum corneum. 

 The legs of birds have scales which are simply epidermal thicken- 

 ings. In mammals, scales are found in a number of different forms. 

 Many such as the beaver and rat have scaly tails; while the scaly 

 anteater (the pangolin) and the armadillo have heavy protective plate- 

 like scales. 



Claws, Nails, and Hoofs. — Claws are present on the tips of the 

 digits of many reptiles, birds, and mammals. They are epidermal struc- 

 tures, originating in the stratum germinativum. In general, they are 

 widened at the base, narrowing toward the tip and curving downward. 

 They resemble an inverted letter V. The upper surface known as 

 the unguis is hard, while below is a smaller ventral plate, the snbungids. 

 This is pinched between the edges of the unguis. 



Fig. 23. — Comparative structure of claws, hoofs, and nails of mammals. A, 

 Longitudinal section of claw; B, longitudinal section of hoof; C, longitudinal section 

 of nail; D, ventral view of claw; E, ventral view of hoof; F, ventral view of nail. 

 Unguis stippled; subunguis hatched; unmodified epidermis, clear; phalanges, black. 

 (Modified from various sources.) 



In its simplest form this describes the claw of the reptiles. The 

 claws of birds, although assuming many different forms, are quite 

 similar to this. In birds, the claws are usually confined to the toes, 

 but there are forms, such as the Hoactzin of British Guiana, which 

 has claws on the wings. The young utilize these for scrambling about 

 in trees. 



The hoofs and nails found in mammals are modified claws. Nails 

 are flattened structures found at the dorsal portion of the tips of the 

 digits of monkeys, apes, and man. As is common with these struc- 



