OF THE PELVIS. 19 



bits, along its middle, a series of protuberances which, by their union, 

 constitute the crista of the sacrum; above this crest is seen the open- 

 ing of the sacral canal; below are the two branches formed by its 

 bifurcation, the triangular space which terminates the spinal canal, 

 and the tubercles or points called the horns of the sacrum. On 

 either side of the false vertebral spines, are seen the sacral grooves, 

 the posterior sacral holes, and still nearer to the edges of the bone 

 are to be found certain rough surfaces that serve for the attachment 

 of the posterior sacro-iliac ligaments. 



7. Its edges may be divided into two portions: one, superior, 

 very thick, exhibits, on its anterior half, a semilunar articular facette 

 which unites it to the coxal bone; on its posterior half, a hollow, and 

 certain rough protuberances for the attachment of the sacro-iliac 

 ligaments; the other, inferior, thin, almost sharp, serves for the in- 

 sertion of the sacro-sciatic ligaments. 



8. Its base, very broad, looks upwards. On its middle may be 

 seen a plain elliptical surface, situated transversely, inclined more or 

 less backwards, and which is articulated with the last lumbar verte- 

 bra; outwards, and a little forwards, a triangular surface, the lesser 

 wing of the sacrum, which is slightly depressed towards its anterior 

 face, and concurs in forming the internal iliac fossa; lastly, we ob- 

 serve on the posterior surface, the opening of the sacral canal, and 

 the two articular apophyses of the first piece of the sacrum. 



9. Its apex, thin, elliptical, slightly convex, is received into the 

 base of the coccyx. 



10. The sacrum, a simple prolongation of the spine, is formed by 

 the union of five vertebrae. Near forty points of ossification may be 

 observed in it; at birth it is still formed of fifteen pieces, three for 

 each vertebra; but soon afterwards it only exhibits five, which, also, 

 always coalesce before the age of puberty. 



§. II. Of the Coccyx {ossa coccygis). 



11. The coccyx is a sort of rudimental sacrum, whose anterior 

 face almost plane, supports the end of the rectum, while its pos- 

 terior surface, slightly convex, is only separated from the skin by 

 the posterior sacro-coccygeal ligament. Its edges serve as points 

 of attachment for the small sciatic ligament, and ischio-coccygeus 

 muscle; its base, somewhat concave, surmounted laterally by two 

 prolongations resembling horns, is articulated with the apex and cor- 

 nua of the sacrum. Its apex, tubercular and rounded, gives inser- 

 tion to the external sphincter of the anus. 



12. The three or four pieces of which it is composed, mere ves- 

 tiges of an equal number of vertebral bodies, remain for a long 



