THE MAMMALIA 289 



intestine is also of considerable size and length, and in 

 herbivorous animals a large diverticulum, the caecum, is given 

 off at the junction of the small with the large intestine. 



The skeleton is well ossified throughout and presents many 

 characteristic features. The vertebral column is divisible into 

 distinct regions viz. the cervical, dorsal or thoracic, lumbar, 

 sacral, and caudal. The cervical vertebrae are seven in 

 number in all Mammalia, with the following exceptions : sloths 

 of the genus Bradypus, in which there are nine, Cholepus 

 Haufmanni, also a sloth, in which there are six, and the 

 Manatee, in which there are also six. This constancy is the 

 more remarkable when the great differences in the length of 

 neck of different mammals is considered. Even the long- 

 necked giraffe and the whale, in which the neck is practically 

 obsolete, have each seven cervical vertebras. The cervical 

 vertebrae have no free ribs attached to them, but a rib element 

 is present fused to transverse processes springing from the 

 centrum and the neural arch and forming with them the 

 vertebral arterial canal. 



The dorsal or thoracic vertebrae bear movably articulated 

 double-headed ribs. Their number varies in different groups 

 and even in closely-allied species, but commonly twelve or 

 thirteen are present, as in the rabbit. 



The lumbar vertebrae are those free vertebrae in front of the 

 sacrum which do not bear ribs. They are generally to be 

 distinguished by their size and their large flattened horizontal 

 transverse processes. Under the name sacral are commonly 

 included all those vertebrae which are fused together in the 

 pelvic region. Properly speaking, only those vertebrae should 

 be called sacral which are attached to the pelvis by the inter- 

 vention of an expanded rib element. Of these there are, at 

 the most, two in mammalia, and the fused vertebrae behind 

 them belong, strictly speaking, to the caudal series. 



The caudal vertebrae vary in number according to the 

 length of the tail. When many are present they decrease in 

 size and complexity from before backwards, and the hindmost 

 of the series are represented only by elongated centra. 



It is highly characteristic of the vertebrae of mammals that 

 the vertebral centra, as well as the long bones, have separate 

 terminal ossifications called epiphyses (this, however, is not the 

 case in the lowest group of mammals, the Protothcria) that 



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