42 



THE ANATOMY OF VEETEBEATED ANIMALS. 



with, a thick coat of hair. The greater part of the mass of 

 the horns of Oxen, Sheep, and Antelopes, is clue to the epi- 

 dermic sheath which covers the bony core. Where the 

 homy epidermis becomes very thick, as in the hoof of the 

 Horse, and in the horn of the Rhinoceros, numerous long 

 papillse of the dermis extend into it. These papillae, how- 

 ever, are compai-able to the ridges of the bed of the nail, 

 not to the papillae of the hairs. 



JB, 



4§w 



^^ 



Fig. 16. — A, outline of a Pike ( Esox), to show the fins : P, pectoral; 

 r, ventral ; A, anal ; C, caudal ; D, dorsal, fins. Op., operculum ; 

 P.Op.,preoperculum ; Br., branchiostegalrays.—B, scales of the der- 

 mal e.\oskeIeton of the same fish. 



The dermal exosheleton arises from the hardening of the 

 dermis; in the majority of cases by the deposit of bone- 

 earth, in more or less completely-formed connective tissue, 

 though the resulting hard tissue has by no means always the 

 structure of bone. It may happen that cartilage is de- 

 veloped in the dermis ; and, either in its primary state, or 

 ossified, gives rise to exoskeletal parts. 



No dermal exoskeleton (except that of the fin-rays) is 

 found in the lowest fishes, Amphioxiis and the Marsipo- 

 branchii. In most Teleostei the integument is raised up 

 into overlapping folds; and, in these, calcification takes 



