42 THE ANATOMY OF VERTEBRATED ANIMALS. 



in the dorsal region, or at the extremity of the body, or on the 

 ventral aspect, behind tlie anus. Ordinary fin-rays are com- 

 posed of a hornlike, or more or less calcified, substance, and 

 are simple at the base, but become jointed transversely, and 

 split up longitudinally, toward their extremities (Fig. 6). 

 Each fin-ray consists of two nearly equal and similar parts, 

 which cohere bv their applied faces for the greater part of 

 their extent ; biat, at the base of the rays, the halves commonly 

 diverge, to embrace, or more or less completely coalesce with, 

 cartilaginous or osseous elements of the exoskeleton. In the 

 median fins, these are the interspinous cartilages, or bones, 

 which lie between the fin-rays and the superior or inferior 

 spines of the vertebrae. In the paired fins, they are radial or 

 basal, cartilaginous or osseous, elements of the endoskeleton. 



The Amphibia in general are devoid of dermal exoskeleton, 

 but the CcerAlim have scales like those of fishes. Ceratophrys 

 has plates of bone developed in the dorsal integument, which 

 seem to foreshadow the plates of the carapace of the Ghdonia; 

 and the extinct Labyrinthodonts possessed a very remarkable 

 ventral exoskeleton. 



The Ophidia have no dermal exoskeleton. Many Lizards 

 have bony dermal plates corresponding in form and size with 

 the epidermal scales. All Grocodilia have such bony plates 

 in the dorsal region of the body and tail ; and in some, such 

 as the Jacares and Caimans, and the extinct Teleosauria, they 

 are also developed in the ventral region. In these animals 

 there is a certain correspondence between the segments of the 

 exoskeleton and those of the endoskeleton. But the dermal 

 exoskeleton attains its greatest development in the Chelonia, 

 and will be particularh' described under the head of that order. 



In the Mammalia the development of a dermal exoskeleton 

 is exceptional, and occurs only in the loricated Edentata, in 

 which the dorsal region of the head and body, and the whole 

 of the tail, may be covered with shields of dermal bone. 



In connection with the dermis and epidermis, the glandu- 

 lar and pigmentary organs of the integument may be men- 

 tioned. Integumentary glands do not appear to exist in 

 Fishes, but they attain an immense development in some of 

 the Amphibia, as the Frog. Among Reptilia, Lizards fre- 

 quentljr present such glands in the femoral and cloacal regions ; 

 and, in Crocodiles, integumentary glands, which secrete a 

 musky substance, lie beneath the jaw. In Birds they attain a 

 considerable size in the uropygial gland ; and, in Mammalia^ 

 acquire a large development in connection with the sacs of the 



