SACRUM. 



19 



Fig. 10." 



of the sacro-iliac articula- 

 tion ; the third is large, 

 and gives attachment to the 

 oblique sacro-iliac ligament ; 

 the fourth and fifth are 

 smaller, and serve for the 

 attachment of the sacro-is- 

 chiatic ligaments. The la- 

 teral border of the sacrum 

 presents superiorly a broad 

 and ear-shaped (auricular) 

 surface to articulate with 

 the ilium ; and inferiorly a 

 sharp-edge, to which the 

 greater and lesser sacro-is- 

 chiatic ligaments are at- 

 tached. On the superior 

 border, in the middle line, 

 is an oval articular surface, 



which corresponds with the under part of the body of the last lumbar 

 vertebra ; and on each side, a broad triangular surface which supports 

 the lumbo-sacral nerve and psoas magnus muscle. Immediately be- 

 hind the vertebral articular surface is the triangular entrance of the 

 sacral canal ; and on each side of this opening an articular process, 

 which looks backwards and inwards, like the superior articular pro- 

 cesses of the lumbar vertebra?. In front of each articular process is an 

 intervertebral notch. The inferior extremity of the bone presents a 

 small oval surface which articulates with the coccyx ; and on each side 

 a notch, which, with a corresponding notch in the upper border of the 

 coccyx, forms the foramen for the transmission of the fifth sacral nerve. 

 The sacrum presents some variety in respect of curvature, and of 

 the number of pieces which enter into its structure. The curve is 

 often very slight, and is situated only near the lower part of the bone ; 

 while in other subjects it is considerable, and occurs at the middle of 

 the sacrum. The sexual differences in the sacrum relate to its greater 

 breadth, and the greater angle which it forms with the rest of the ver- 

 tebral column in the female, rather than to any peculiarity in shape. 

 It is sometimes composed of six pieces, more rarely of four, and occa- 

 sionally the first and second pieces remain permanently separate. 



* The sacrum seen upon its anterior surface. 1, 1. The transverse lines 

 marking the original constitution of the bone of four pieces. 2, 2. The ante- 

 rior sacral foramina. 3. The promontory of the sacrum. 4. The ear-shaped 

 surface which articulates with the ilium. 5. The sharp edge to which thesacro- 

 ischiatic ligaments are attached. 6. The vertebral articular surface. 7. The 

 broad triangular surface which supports the psoas muscle and lumbo-sacral 

 nerve. 8. The articular process of the right side. 9. The inferior extremity, 

 or apex of the sacrum. 10. One of the sacral cornua. 1 1 . The notch which is 

 converted into a foramen by the coccyx. 



