CHAPTER XXII. 



GENERAL ACCOUNT OF THE SKELETON IN 

 MAMMALIA. 



THE EXOSKELETON AND VERTEBEAL COLUMN. 



EPIDERMAL EXOSKELETON. 



Hair, which forms the characteristic Mammalian exo- 

 skeleton varies much in different animals, and in different 

 parts of the same animal. A large proportion of mammals 

 have the surface fairly uniformly covered with hair of one 

 kind only. In some forms however there are two kinds of 

 hair, a longer and stiffer kind alone appearing on the surface, 

 and a shorter and softer kind forming the under fur. In 

 most mammals hairs of a special character occur in certain 

 regions, such as above the eyes, on the margins of the 

 eyelids, and on the lips and cheeks, here forming the vibrissae 

 or whiskers. 



Sometimes as in Hippopotamus, Orycteropus and the Sirenia, 

 the hair, though scattered over the whole surface, is extremely 

 scanty, while in the Cetacea it is limited to a few bristles 

 in the neighbourhood of the mouth, or may even be absent 

 altogether in the adult. In most mammals the hairs are 

 shed and renewed at intervals, sometimes twice a year, before 

 and after the winter. The vibrissae or large hairs which 

 occur in many animals upon the upper lip, and the mane and 

 tail of Equidae are probably persistent. 



