MAMMALS. 557 



which secrete the milk, with which the mother feeds her young, 

 and in being viviparous. Their skin, moreover, is not covered 

 with feathers, but commonly with hair; only some have horny 

 scales or shields, which cover the back or also the feet and the 

 upper part of the head. 



The skeleton of mammals deserves, in the first place, our con- 

 sideration. The vertebral column is, with the exception of the 

 cetaceous animals, divided into the same regions as in man, viz. 

 the cervical, the dorsal, the lumbar, the sacral and the caudal. In 

 the cetacea, numerous vertebrae (in the porpess four or five and 

 forty) succeed to the dorsal vertebrae, and compose the tail, in 

 which the lumbar region cannot be distinguished from the sacrum. 

 Although the neck in the various species differs greatly in length, 

 still it is found to consist in this class, with two or three excep- 

 tions, constantly of seven cervical vertebrae. The three-toed sloth 

 (Bradypus tridactylus) has nine cervical vertebrae 1 ; in Manatus 

 australis there are commonly six. Consequently the length of the 

 neck does not depend upon the number of its vertebrae 2 . In the 

 ungulate animals the length of the neck corresponds to that of the 

 fore-legs 3 . There are generally thirteen dorsal vertebrae present, as 

 in most of the ruminants, and many rodents, in most species of the 

 genus Felis, in the dog, the fox, &c.; seldom only are there fewer 

 than twelve (eleven in some bats and in species of Dasypus; in one 

 species of this genus, according to CUVIER, there are only ten, 

 which appears to be a solitary exception). Just as rare is it 

 almost that there should be more than fifteen; the horse has 



1 This remarkable exception was first noticed by WIEDEHAITN, and by EOUSSEAU, 

 rosector of the Museum of the Garden of plants at Paris; see Ann. du Mus. V. 



[804, p. 20 1. Bradypus torquatus has 8 cervical vertebrae; Bradypus didactylus has 

 usual number (7). Although on the two lowest cervical vertebrae in Bradypm 

 tylus traces of ribs are found (see TH. BELL Transact, of the Zool. Soc. I. p. 113), 

 it these vertebrae are not on this account to be considered as dorsal. (The transverse 

 processes of all the cervical vertebrae in the mammals and also in man have a rudimentary 

 ib on the anterior root.) 



2 The neck in man forms about one-seventh of the length of the whole verbetral 

 >lumn ; in the giraffe three-sevenths. 



3 The elephant forms a remarkable exception to this rule, and the proboscis, which 

 performs the office of a hand (ARISTOTELES Historia anim. Lib. 11. cap. i), com- 

 pensates the absence of a long neck, which would be ill able to support the heavy 



of the head. Comp. CICERO De natura Deor. Lib. n. cap. 50. 



