18 



BONES OF THE TRUNK. 



The first is the smallest ; the lydrd has the longest transverse 

 process; the fifth has a wedge-shaped body. 



SACRUM. 



Is triangular, and originally consisted of five pieces; its 



Fig. 4. 



terior surface is concave, and 

 has four Ibnnel-shaped holes^^ ^ 

 on each side transmitting the 

 anterior branches of the sacral 

 nerves. Its posterior surjme is 

 rough and convex, and contains 

 the representations of spinous 

 and oblique processes. A fis- 

 sure usually exists in place of 

 the fourth and fifth spinous pro- 

 cesses. There are four fora- 

 mina on each side, smaller than 

 those in front, for the transmis- 

 sion of the posterioi' branches of 

 the nerves. The base has a 

 large oval articular mark' upon which rests the last lumbar ver- 

 tebra, two grooves completing the intervertebral foramina ; and has 

 also two oblique processes. ^ The apex^ is blunt and has a transverse 

 articular surface^ for the coccyx. The sides are rough, broader 

 above than below, having a large articular mark for the innominata ; 

 behind this surface arise muscles of the back, and below it the sacro- 

 iliac ligaments. The sacral canal runs through the length of the 

 sacrum. It is triangular and larger above than below f is continuous 

 with the spinal canal and contains the cauda equina ; with it com- 

 municate the foramina transmitting the nerves. 



COCCYX. ' 



coccyx is flat and triangular, having its base upwards. It 

 consists of three or four bones united usually in the 

 same curve as that of the sacrum. The pieces are 

 frequently united with each other and (he sacrum. 



The first piece is the largest, and has two articular 

 marks; behind, it has two cornva ;'^^^ on its side are 

 grooves*, 5 which with the sacrum complete the canal 

 for the fifth sacral nerve. The last 2nece^ is a mere tu- 



The sides of the coccyx give origin to muscles and ligaments. 



PELVIS. 



The pelvis consists of ihe sacrum^ coccyx^ and the two innominata 

 or hip bones. 



