360 THE ANIMAL KINGDOM. 



rnalia y white in colour. Epidermic structures in the shape of nails, claws, 

 or hoofs, protect the terminal joints of the hand and foot, except in Cetacea 

 and certain fingers in the Chiroptera. Other instances of epidermic skeletal 

 structures are the imbricated scales covering the body and tail in Manis 

 among Edentata, or the under side of the tail in certain flying Rodents 

 (Anomalurus) ; the flat scales placed edge to edge on the tails of some 

 Rodents, e. g. the Beaver (Castor], of certain Insectivora (Ptilocercus) and 

 Metatheria ; the spines of some Insectivora (the Hedge-hog, Erinaceus], 

 Rodentia (the Porcupines, Hystricidae\ and of Echidna among Prototheria ; 

 the horns as opposed to their bony supports, the horn-cores, of hollow- 

 ^horned Ruminantia (Cows, Sheep, Goats, Antelopes) ; the nasal horns of the 

 Rhinoceros ; the thickened epidermis of the callosities, hair-less patches of 

 skin occurring in different regions of the body, e. g. over the ischial tuber- 

 osities in Apes ; and the whale-bone plates implanted in the gum of the 

 Baleen Whales. A bony dermal skeleton is found only in the Dasypodidae 

 and the extinct Glyptodontidae among Edentata in the shape of scutes or 

 plates covered by a thickened epidermis. The antlers, or bony frontal 

 outgrowths, of the Deer, which are shed and renewed annually, must be 

 reckoned under the same head. The glands of the integument are the 

 following : sebaceous glands connected with the roots of the hairs ; sudori- 

 parous glands opening on the surface of the skin, and rarely wanting, e. g. 

 in Cetacea, as well as certain other special glands, e. g. the Meibomian 

 glands of the eyelids, the lacrymal glands ; and glands known as sub- 

 orbital, anal, inguinal, &c., according to position. The mammary glands 

 characteristic of the class, which secrete the milk, are probably modified 

 skin-glands. Their ducts open on an area which is usually raised into a 

 more or less prominent papilla the true teat. In Ungulata, however, this 

 area lies at the bottom of a tubular depression produced by the growth of 

 a surrounding wall forming a false teat. The number of teats present 

 varies according to the number of young usually produced at a birth, from 

 two, e. g. in the Primates, to twenty-two as a maximum in Centetes among 

 Insectivora. When numerous they usually extend in two rows from the 

 pectoral to the inguinal region : when few they are restricted to the pectoral, 

 abdominal or inguinal regions. In all Mammalia except the Hare, Lepus 

 timidus, a layer of adipose tissue, the panniculus adiposus, sometimes attain- 

 ing great thickness as in the blubber of the Cetacea and Seals, is interposed 

 beneath the skin and underlying muscles and bones ; and in most instances 

 there is a well developed system of skin-muscles. 



The bones of the skull, with the exception of the lower jaw, the 

 auditory ossicles, and hyoid, are united by sutures which persist as a rule. 

 The two occipital condyles are formed by the exoccipital bones, but in 

 some Mammals in part by them, in part by the basi-occipital. The prae- 

 maxillary, maxillary and palatine bones possess palatal plates which con- 



