72 SPECIAL ANATOMY. 



Base presents : a superior, oval articular surface, turned towards the infe- 

 rior surface of the body of the last Lumbar vertebra ; behind this, a triangular 

 opening, formed of two planes, behind, a spirious process; two triangular 

 lateral surfaces, which help to form the great pelvis ; notches to form the last 

 iutervertebral foramina; two superior oblique processes. 



Apex/ blunt, with a transversely lying articular surface for the coccyx, 

 behind the termination of the sulcus of the sacrum, two sacral cornua, which 

 are the most inferior articular processes. 



Surfaces : 



a. Anterior, concave, with four elevated transverse lines, marking the 

 points of junction of the vertebrae spur. / on either side four anterior sacral 

 foramina, for nerves and vessels. In this curvature lies the Rectum; m. 

 pyriformis arises external to and between these foramina. 



b. Posterior, close beneath the skin in the centre, convex; in the middle 

 line the Crista Sacralis, a continuation of the Spinous processes, which, par- 

 tially divided, has close to it, laterally, two fiat furrows and four foram. sacral, 

 post., for the nervi sacr. posterior. Besides, the united oblique processes pro- 

 jecting more strongly outwards, and the transverse processes, alse sacral, in one 

 piece. 



c. Lateral surfaces : triangular, above broad, below narrow, oblique from 

 before to behind, and from without inwards. Anteriorly a semilunar arti- 

 cular surface, fades auricularis, for the Hip bone,- behind it rough elevations 

 for the post, sacro-iliac ligaments. Below on the indented borders the Sacro- 

 Ischiatic ligaments. 



Canalis sacralis is the termination of the can. spinalis triangular, above 

 broad, below narrow, and terminating in a groove. Into it the anterior and 

 posterior sacral foramina open ; out of it the Sacral nerves come forth. 



80. 2. Os coccygis, fundament, tail bone, 



consists of four united flat tubercles, the size of which diminishes 

 downwards ; is flat, triangular, above, broad at the extremity of 

 the Sacrum, below, pointed and free. 



Direction : usually that of the sacrum, forming, sometimes with 

 this bone a right, indeed, even an acute angle. Important in 

 obstetricy. 



Muscles : glutseus maxim., coccygeus, levator et sphincter ani. 



Basis, the most superior piece, often united to the os sacrum. Behind two 

 cornua stand upwards from it; externally two notches, for the fifth pair of 

 Sacral nerves. 



Apex sometimes forked, or aside from the middle line. For the levator 

 Ani. 



Surfaces : Anterior. Before it lies the rectum. 



Posterior, close beneath the skin, serves for the attachment of the 



m. glutseus Max. 



Sides, narrow, indented, rough, for Sacro-lschiatic ligaments. 

 Canalis Spinalis, Canal for the Spinal cord, is formed by the foramina spi- 

 nalia lying over one another ; it follows all the curvatures of the vertebral 

 column, the diameters of which, however, differ from those of the canal. 

 Commencement: at the great Occipital foramen. 

 Termination: in the sacrum. 



