VEETEBEAL COLUMN. 401 



2. The thoracic vertebrae are five in number. The three 



anterior ones are fused together and with the last 

 cervical vertebra : their centra, arches, and various 

 processes being confluent, and the neural spines and 

 hypapophyses forming continuous dorsal and ventral 

 ridges. 



The fourth thoracic vertebra is free ; and the 

 fifth is fused with the first sacral vertebra, its trans- 

 verse processes abutting against and fusing with the 

 ilia. 



3. The sacrum consists of fourteen or fifteen vertebrae, fused 



together and supporting the ilia. It may be divided 

 into the following regions. 



a. The three anterior sacral vertebrae are firmly fused 



together, and with the last thoracic vertebra. 

 They have stout transverse processes, which abut 

 against the ilia, and which in the first one 

 two are single, but in the third are divided into 

 dorsal and ventral portions, the latter being very 

 stout and projecting directly outwards from the 

 broad centrum. The neural spines of these ver- 

 tebrae are fused to form a vertical crest of bone, 

 which is continuous in front with that of the 

 last thoracic vertebra, and fused along its edge 

 with the dorsal edges of the ilia. 



b. Behind these come four or five shorter vertebra, 



with broad centra fused together. Their trans- 

 verse processes, which have no ventral elements, 

 are united to form bony plates, which support the 

 ilia along their outer margins. 



Between the bodies of these vertebra and the 

 ilia are the deep hollows in which lie the middle 

 lobes of the kidneys. 

 0. Next come seven vertebra, the centra of which are 

 compressed laterally in the anterior ones, and 

 dorse -ventrally in the hindmost two or three. 

 The transverse processes, except in the last, are 



D D 



