THE SPINE. 87 



regular concavity; in some subjects, nevertheless, it is flat. This 

 surface is pierced on each side by four holes, which communi- 

 cate with the spinal cavity and transmit the anterior nerves of 

 the cauda equina. Beneath each range of holes is a notch, which 

 by the corresponding one of the* coccyx, is converted occasion- 

 ally into a perfect foramen for the thirtieth spinal nerve, or for 

 the fifth of the sacrum. These foramina diminish in size, from 

 the higher to the lower: their orifices are funnel-shaped, and di- 

 rected obliquely outwards. Horizontal ridges of bone, marking 

 the original separation of the false vertebrae, connect the holes 

 of the two sides. 



The false vertebrae decrease in size from above, which is ma- 

 nifested by the successive approach of the foramina, and of the 

 horizontal ridges. The first of them has almost the same verti- 

 cal diameter as the last of the loins, besides its great increase of 

 magnitude by the lateral extension of its base. 



The posterior face of the sacrum is very convex and rough, 

 and is equally divided by its spinous processes. The processes 

 belonging to its three upper sections or bones, are for the most 

 part well marked, and decrease in length from the first. The 

 fourth spinous process is resolved into two tubercles, and the 

 fifth is fairly separated also into two tubercles, by an angular 

 fissure, with its base downwards and open. This fissure, it may 

 be remarked, sometimes invades the fourth spinous process, and 

 even the third, and in some rare eases runs the whole length of 

 the posterior surface of the bone, leaving a gap from one end to 

 the other. The upper margin of the posterior face of the sacrum 

 presents on each side an oblique process for articulating with 

 the lower oblique processes of the last lumbar vertebra. Just 

 above the upper spinous process is a deep notch, between which, 

 and the last lumbar vertebra, is a very large vacuity, or gap, ex- 

 posing the spinal canal. 



On each side of the spinous processes are also four foramina, 

 smaller and thinner than those in front, and for the passing of 

 the posterior nervous cords from the cauda equina. At their in- 

 ternal margins some small and obscure risings of bone are per- 

 ceptible, which may be considered the rudiments of oblique pro- 

 cesses. On the outer side of these foramina, there are several 

 more strongly marked tubercles, from which the sacro-iliac liga- 



