130 



MAMMALIAN ANATOMY 



The last lumbar vertebra may be always recognized by the 

 small cephalo-caudal diameter of its laminae and by its pointed 

 spinous process. 



HUMAN SACRUM. 



The human sacrum (Figs. 91, 92) is composed of five coalesced 

 vertebrae ; hence it is, relatively, a larger mass than the sacrum of 



FIG. 92. 



FIG. 91. 



SACRUM. FRONT VIEW. 



1, transverse ridges, indicating the original 

 separation of the bone into five segments; 2, 

 sacral foramina; 3, promontory; 4, articular 

 surface for the hip-bone ; 5, sacral border of the 

 saero-sciatic notch ; 6, base of the sacrum, with 

 its articular surface for the last lumbar verte- 

 bra ; 7, wing of the sacrum : 8, superior artic- 

 ular process ; 9, apex of the sacrum, with its 

 articular surface for the coccyx; 10, cornu of 

 the last vertebral arch; 11, notch for the last 

 sacral nerve. 



SACRUM. BACK VIEW. 



1, rudimental spinous processes; 2, 2, sacral 

 canal; 3, 3, rudimental articular processes; 4, 

 cornu; 5, sacral foramina; 6, 6, rudimental 

 transverse processes : 7, articular surface for 

 the hip-bone : 8, sacral border of the sacro- 

 sciatic notches ; 9. articular surface for the last 

 lumbar vertebra; 10, superior articular pro- 

 cesses for the latter bone ; 11, apex of the 

 sacrum ; 12, rough surface on the wing of the 

 sacrum, for the sacro-iliac ligaments. 



the cat, and presents, instead of twelve, sixteen sacral foramina, 

 four on each side of the ventral surface and four on each side of 

 the dorsal surface. It has five tubercular spinous processes. 



The auricular surface, for articulation with the innominate bones, 

 is longer and narrower, extending on the lateral surfaces of the first 

 three vertebrae. 



The dorsal surface is rougher and the strip lateral to the sacral 

 foramina is wider ; its cephalic portion, known as the sacral 

 tuberosity, is formed at the expense of the lateral surface. 



The human sacrum is decidedly curved in the cephalo-caudal 

 line, the concavity facing the ventral side. It is less curved and 

 is wider in women than in men. 



