32 



A MANUAL OF ANATOMY 



row of spines there is a solid mass formed by the ankylosed lamina}, 

 which forms the sacral groove for the origin of a portion of the 

 multifidus spinas. External to this groove there is a row of for- 

 amina, four in number at either side, called the posterior sacral 

 foramina, which are smaller than the anterior, and, like them, 

 diminish in size from above downwards. These foramina open 

 outwards and backwards from the intervertebral foramina (by 

 which they communicate with the sacral canal), and transmit the 



Rudimentary Articular Processes (fused) 



Superior Articular ProccGs 



Ligamentous Surface 



Auricular Surface 



Multifidus 



SpinEE 



Transverse Process 



(rudimentary) 



Gluteus Maximus 



Outlet of Sacral Canal , — 



Notch for 5th Sacral Nerve 



2nd Posterior Sacral 

 Foramen 



'*■ Inferior Lateral Angle 



Sacral Cornu 



Fig. 23. — The Sacrum (Posterior View). 



posterior primary divisions of the first four sacral nerves. It is 

 to be noted that they lie directly behind the anterior foramina. 

 Internrd to the posterior foramina, and encroaching upon them, 

 there is a row of small projections which represent the articular 

 processes of the sacral vertebrae. The lower pair, which belong to 

 the fifth sacral vertebra, are prolonged downwards as two plates 

 which end in enlargements. These are called the sacral cornua, and 

 they are connected with the cornua of the first coccygeal vertebra, 

 usually by ligaments, but sometimes by osseous union. The 



