77/ A' SI'IXAL COLUMN 17 



Tlif apex is directed downwards and forwards, and is formed l)y the inferior 

 aspect of tlie l)ody of the tifth sacral vertel)ra; it articulates by means of an inter- 

 vertebral disc Avith the coccyx. In advanced life the coccyx and sacrum ankylose 

 at this spot. 



The lateral surface i>rpsents in the upper two-thirds a broad irregular tract 

 called the auricular process, which is rough and, in the recent state, covered 

 with til)ro-cartilage for union with the ilium. The margins are rough for liga- 

 ments. Below the auricular surface each lateral l)order forms a tuberosity and 

 gives attachment to the greater and lesser sacro-sciatic ligaments. Near the 

 extremity it presents a notch which is converted into a foramen by articulation 

 with the coccyx. Through the space tlius enclosed, the anterior branch of the fifth 

 sacral nerve issues. Sometimes the foramen is represented by a notch even when 

 the sacrum and coccyx are articulated. The middle of the sacrum is occupied by 

 a continuation of the spmal canal. It is triangular in form at the base, and flat- 

 tened towards the apex. It lodges the terminal branches of the cauda equina, the 

 filum terminale, and the lower extremity of the dura mater. 



The sacrum exhibits sexual and racial differences. In the female it is usually 

 wider, much less curved, and is directed more obliquely backwards, than in the 

 male, and in the lower races the sacrum is relatively kmger than in the higher. 



Muscles. — The following muscles a-re attached to the sacrum: — Pyriformis, 

 coccvgeus, iliacus, latissimus dorsi, multifidus spina?, erector spina?, gluteus maxi- 

 mus"; and the occasional muscles, namely, curvator coccygis, extensor coccygis, 

 and the agitator cauda?. 



Ligaments. — Anterior and posterior common ligaments of the spine; anterior 

 and posterior sacro-coccygeal ; greater and lesser sacro-sciatic, anterior and posterior 

 sacro-iliac, two capsular, ligamenta subflava, and the supraspinous. 



THE COCCYX 



The coccyx in the adult is made up of four and occasionally five vestigial ver- 

 tebne ankylosed to one another. Rarely the number of segments is reduced to 

 tln-('c. The first two segments contain, in addition to the body of a vertebra, traces 

 of articular and transverse processes : the rest are mere nodules of bone, repre- 

 senting centra. The anterior surface gives attachment to the anterior sacro-coccy- 

 geal ligament; and near its tip to the levator an! : it is in relation with the posterior 

 surface of the second part of the rectum. 



The posterior surface is convex, and presents above a laterally projecting ])rocess, 

 the rudimentary transverse process of the first segment, and along its margin affords 

 attachment to the f/liitfiis iiHixiiiins muscle. 



The lateral borders are thin: they receive parts of the greater sacro-sciatic liga- 

 ments and of the cocny^f'/s- muscle. The base has an oval facet for the fifth sacral 

 vertebra, and presents the two long coccygeal cornua, formed by the remains of 

 the pedicles and superior articular processes of the first segment, for the posterior 

 sacro-coccygeal ligament. The junction of the coccyx and sacrum completes the 

 foramen of exit for the fifth sacral nerve. In many skeletons the foramen is incom- 

 plete externally. The apex is rounded and gives attachment to the sjihlnder ani, 

 and in front to the levator ani muscles on each side of the median line. 



THE SPINAL COLUMN IN GENERAL 



^^'lu■n the various vertebrfe are in their relative positions, the whole is termed 

 the spinal column. It occupies the median line of the posterior aspect of the trunk. 

 Suixriorly, it supports the head; laterally, it gives attachment t(» the ribs; these in 

 their turn receive the weight of the upjjcr limbs. Inferiorly, the sacrum affords 

 attachment to the innominate bones, by which the weight of the trunk is trans- 

 mitted to the lower limbs. The spinal colunm is the axis of the skeleton. 



It varies in length in different persons, but on an average it measures, from the 

 atlas to the tip of the coccvx, following the curve. 70 cm. (2S"j. Of this, the 

 2 



