18 SACRUM. 



from that point towards the extremities of the column ; hence im- 

 perfection of the bodies occurs either in the upper or lower ver- 

 tebrae. 



Attachment of muscles. To the atlas are attached ten pairs of 

 muscles ; the longus colli, rectus anticus minor, rectus lateralis, rectus 

 posticus minor, obliquus superior and inferior, splenius colli, levator 

 anguli scapulae, first interspinales, and first intertransversales. 



To the axis are attached twelve pairs, viz. : the longus colli, inter- 

 transversales, obliquus inferior, rectus posticus major, supraspinalis, 

 interspinales, semi-spinalis colli, multifidus spinae, levator anguli sca- 

 pulae, splenius colli, transversalis colli, and scalenus posticus. 



To the remaining vertebra collectively, thirty-three pairs ; viz, pos- 

 teriorly^ the trapezius, latissimus dorsi, levator anguli scapulae, rhomboi- 

 deus minor and major, serratus posticus superior and inferior, splenius, 

 sacro-lumbalis, longissimus dorsi, spinalis dorsi, cervicalis ascendens, 

 transversalis colli, trachelo-mastoideus, complexus, semi-spinalis dorsi 

 and colli, multifidus spinae, supraspinalis, interspinales, intertransver- 

 sales, levatores costarum ; anteriorly, the rectus anticus major, longus 

 colli, scalenus anticus and posticus, psoas magnus, psoas parvus, quad- 

 ratus lumborum, diaphragm, obliquus internus and transversalis. 



THE SACRUM is a triangular bone, situated at the lower extremity 

 of the vertebral column, and formed by the consolidation of five false 

 vertebrae. It is divisible into an anterior and posterior surface, two 

 lateral and a superior border, and an inferior extremity. 



The anterior surface is concave, and marked by four transverse lines, 

 which indicate its original constitution of five separate pieces. At the 

 extremities of these lines, on each side, are the four anterior sacral 

 foramina, which diminish in size from above downwards, and transmit 

 the anterior sacral nerves. The projection of the superior piece is 

 the sacro- vertebral angle or promontory. 



The posterior surface is narrower than the anterior and convex. 

 Upon the middle line is a rough crest formed by the rudiments of four 

 spinous processes, the fifth remaining undeveloped and exposing the 

 lower termination of the sacral canal. Immediately external to and 

 parallel with the median crest, is a range of five small tubercles which 

 represent the posterior tran verse processes of the true vertebrae ; beyond 

 these is a shallow groove in which the four posterior sacral foramina 

 open, and farther externally, a range of five tubercles corresponding 

 with the anterior or costal transverse processes of the lumbar vertebrae. 

 The lowest pair of the posterior transverse tubercles bound on each 

 side the termination of the sacral canal, and send, each, a process down- 

 wards to articulate with the coccyx. The two descending processes 

 are the sacral cornua. The posterior sacral foramina are smaller than 

 the anterior, and transmit the posterior sacral nerves. Of the anterior 

 transverse tubercles ihe first corresponds with the angle of the superior 

 border of the bone ; the second, is small, and enters into the formation 



