. Chordate morphology. Morphology (Animals); Chordata. mammary gland ducts. Lactation hairs may surround the area of the nipple. The position and number of the mam- mary glands varies. Reptiles The skin of the reptile is covered by keratin scales, each of which covers an epidermal and dermal scale elevation. The scale cover is continuous over the entire body but thin- ner in the grooves between the scales. Periodically it is shed, a process called ecdesis (Figure 8-6). Close examination of the lizard's skin shows at least two types of scales; the large scales usually described and smaller ones
. Chordate morphology. Morphology (Animals); Chordata. mammary gland ducts. Lactation hairs may surround the area of the nipple. The position and number of the mam- mary glands varies. Reptiles The skin of the reptile is covered by keratin scales, each of which covers an epidermal and dermal scale elevation. The scale cover is continuous over the entire body but thin- ner in the grooves between the scales. Periodically it is shed, a process called ecdesis (Figure 8-6). Close examination of the lizard's skin shows at least two types of scales; the large scales usually described and smaller ones lying between these (Figure 8-7). In Iguana, the small scales are quite pointed. Histological examination reveals sen- sory structures, the prototrichs, on some large and many small scales (Figures 8-8, 8-9). The protothrix (singular of proto- trichs) of the reptile has been described as the precursor of the hair of the mammal, as the term itself declares. It is quite possible that the small scales margining the large scales are the forerunners of both hair and feathers. The homology of these scales with the feather is most probable. Osteoderms sometimes lie in the dermis below the scale. These bony plates may have the same distribution as the keratin scales or be quite independent of them. The bony plates (osteoderms) are tied into the dermis by Sharpey's fibers, just as the scales of fishes are. Osteoderms are typical of the crocodilian and some lizards. In the turtle, the cara- pace is formed basically of osteoderm and rib contributions. These are covered externally by horny epidermal scales; the epidermis lies between these scales and the bony base. The epidermis of the reptile is generally without glands, although special glands occur in different reptiles; the lizard has femoral glands along the posteroventral margin of the thigh (Figure 8-6). The alligator has inframandibular and cloacal scent glands which are functional during the repro- ductive period. The development
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