THE SPINAL COLUMN AND BACK. 



153 



present in every vertebra. In the cervical vertebrae the anterior 

 part of the transverse processes represents a costal process, but 

 only in the 6 th (sometimes) and 7 th is the costal process formed 



spine 

 trans, proa 



costal facet 

 centrum 



trans, proa 



dors, head 

 rib 



vent, head 



Flo. 123. — The Bicipital Rib of a Lower Vertebrate (crocodile). 



by a separate- centre of ossification. The costal process of the 7 th 

 may develop into a rudiment or even a fully formed rib which 

 reaches the sternum. In the lumbar vertebrae only the first shows 

 a separate centre for the formation of the costal process ; it fuses 

 with the tip of the transverse process in the later months of foetal 

 life ; in the other lumbar vertebrae the tips or perhaps the whole 

 of the transverse processes represent costal processes. The 12th 

 dorsal rib varies widely in size ; it may be six inches or ten 

 long or reduced to a mere vestige. 



In the 1st, 2nd and 3rd sacral vertebrae the costal processes are 

 large and have their own centres of ossification. Their cartila- 

 ginous bases fuse early to form the greater part of the lateral 

 masses of the sacrum (Fig. 115). The part of the lateral mass 



neural arch 

 trans, proa 

 cost, proa 



epiphysis 

 centrum 



Fia. 124.— A section to show the Nature of the Elements composing the Sacrum. 



formed by the costal processes is shown in Fig. 124. The costal 

 processes are absent in the 4th and 5th sacral and all the 

 coccygeal vertebrae. The two lateral epiphyseal plates on each 

 •side of the sacrum are new and independent formations. 



The Accessory Processes are found in the lumbar and lowest two 



