Vertebral Column 



39 



and ends just below the fourth foramen in the inferior lateral angle, while the last 

 segment projects below this as a blunt apcx. it 



The convex posterior surface (Fig. 32) has in the middle the fused neural arches 

 that cover in the sacral canal : the canal is open above and below, and at the lower 

 end one or two of the neural arches may be partly deficient. Various bony projections 



s.c. 



FIG. 32. A. posterior aspect of sacrum. The arrows pass through the upper 

 and lower openings into the sacral canal. 7>. transverse processes; 

 S.C. crest made by spinous processes; A.C. articular crest; S.G. sacra 

 groove. B. view from above, showing the upper aspect of the lateral 

 masses, forming the alae. a. impression for nerve ; b. roughened markings 

 for ligamentous fibres. 



may be recognised as lying in series with the processes of the true vertebrae. In the 

 middle line is a row of connected spines, the spinal crest (S.C.), outside this is a narrow 

 sacral groove (S.G.), floored by fused laminae and bounded laterally by a row of low 

 tubercles in series with the articular processes, the articular crest (A.C.) ; outside these 

 are the four posterior sacral foramina, and then the back aspect of the lateral mass. 

 The sacral groove and its neighbouring processes give origin to post- vertebral muscles, 

 and the two articular crests end below in the projecting cornua which represent the 



