452 THE VERTEBRATE SKELETON. 



or five vertebrae fused together in the sacral region. In 

 Notary ctes there is extensive fusion in the sacral region, six 

 vertebrae, owing mainly to the great development of their 

 metapophyses, being united with one another, and with the 

 ilia, and the greater part of the ischia. 



In most EDENTATA there is an extensive fusion of verte- 

 brae in the sacral region. This is especially marked in the 

 Armadillos and Megatheriidae, and to a less extent in the 

 Sloths and Aard Yarks. 



In the SIRENIA the vestigial pelvis is attached by ligament 

 to the transverse processes of a single vertebra, which hence 

 may be regarded as sacral. 



In CETACEA there is no sacrum, the vestigial pelvis not 

 being connected with the vertebral column. 



In most UNGULATA the sacrum consists of one large ver- 

 tebra united to the ilia, and having a varying number of 

 smaller vertebrae fused with it behind. 



The same arrangement obtains in most RODENTIA, but in 

 the Beavers (Castoridae) all the fused vertebrae are of much 

 the same size, the posterior ones having long transverse 

 processes which nearly meet the ilia. 



In CARNTVORA there may be two sacral vertebrae as in the 

 Hyaena, three as in the Dog, four or five as in Bears and 

 Seals. 



In INSECTIVORA from three to five are united, while in 

 many CHIROPTERA all the sacral and caudal vertebrae have 

 coalesced. Among PRIMATES, in Man and Anthropoid Apes 

 there are usually five fused vertebrae forming the sacrum, 

 but of these only two or three are connected to the ilia by ribs. 

 In most of the other Anthropoidea there are two or three 

 fused vertebrae, and in the Lemuroidea two to five. 



FREE CAUDAL VERTEBRAE. The free caudal vertebrae 

 vary greatly in number and character. When the tail is well 

 developed, the anterior vertebrae are comparatively short and 

 broad, with well-developed neural arches and zygapophyses ; 



