OSTEOLOGY. 55 



cess of tlie first bone, separating the articulatory surface of 

 the body from those on the anterior margins of the transverse 

 processes, wliicli overhang the grooves inferiorly in a re- 

 markable manner. These surfaces come into contact with 

 those on the posterior margin of the transverse processes 

 of the last lumbar, of which they are the exact counterparts, 

 being almost flat, looking inwards and slightly upwards. 

 They extend to the outei' extremity of this transverse pro- 

 cess, which is sharp, and at its superior surface form 

 angles with rounded roughened surfaces which extend to the 

 extremity on the postero-external part, much expanded, 

 looking upwards, backwards, and outwards, for union with 

 the venter surface of the ilium. They do not occupy the 

 whole of the upper surface, but are continued by a rough- 

 ened ridge, which extends along the lateral part of the 

 bone, becoming smaller and sharper posteriorly, formed by 

 union of the transverse processes of the other sacral bones ; 

 it affords attachment to the sacro-sciatic ligament. Both 

 above and below this ridge is a series of foramina, four in 

 number, decreasing in size from before backwards for 

 passage of the branches of the sacral nerves, the superior 

 branches through the superior foramina, the inferior 

 branches through the inferior foramina, through which 

 also pass branches of the lateral sacral arteries and veins. 

 Above the superior foramina (supersacral) are a series of 

 small prominences, decreasing in size from before back- 

 wards, produced by the oblique processes of the bones. 

 Higher up are the superior spinous processes, more or less 

 completely united by ossification of the interspinous and 

 interlaminal ligaments, presenting a series of five tuberous 

 prominences, to which triceps abductor femoris, biceps 

 rotator tibialis, ischio -tibialis, and some of the coccygeal 

 muscles, also the lateral sacral ligament and longissimus 

 dorsi are attached. The first spinous process looks almost 

 directly upwards ; the rest have a marked direction back- 

 wards, and decrease in length posteriorly. The inferior 

 surface of the bone anteriorly, on either side, presents a 

 remarkable smooth, irregular concavity, being the under 

 surface of the transverse process ; a rounded neck, extend- 

 ing inwards and backwards, serves to unite this to the 

 main portion, which is formed by the under surfaces of 

 the bodies, as denoted by transverse, irregular ridges, 

 which serve to divide this portion into five flattened parts. 



