SPINAL COLUMN, STERNUM AND RIBS. 15 



Coccygeal vertebrae. — Tliese are 15 to iX in number. The 

 spinal canal is developed in the first three or four. The first 

 one is occasionally united to the sacrum. 



The sternum. — This is located in the front and lower portion 

 of the chest, and extends from Ijefore to behind, it consists of 

 six or seven pieces of cartilaginous bone and has distinct prolonga- 

 tions of cartilage from both the front and rear ends. On each 

 side are articular surfaces for the first eight ribs. 



Ribs. — These usually number 18 pairs, and are described as 

 the first, second, third, etc., beginning with the front pair. They 

 all articulate above with the dorsal vertebrae, the lower ends of 

 the first eight articulate with the sternum by means of cartilages. 

 The remaining ten connect with the sternum by means of long 

 cartilages, each of which rests against the preceding one. The 

 ninth, or first asternal, rib is united rather closely to the eighth 

 which articulates with the sternum. 



FIG. 9. TYPICAL LUMBAR VER- FIG. 10. LATERAL VIEW OF 



TEBRA, FRONT VIEW. THE SACRUM. 



L Body; 2, head: 3, superior spin- 1, Spinal canal, anterior portion; 



ous process; 4, transverse process. 3, superior spinous processes. 



The shaft shows external convex, and internal concave sur- 

 faces and two borders : anterior or front, and posterior or rear. 

 The superior extremity shows a head and a small projection, the 

 tuberosity. These articulate with the dorsal vertebrae as already 

 explained. The inferior extremity of each rib is somewhat concave 

 for the cartilage which connects it with the sternum or other car- 

 tilages. The ribs increase in width up to the sixth, then decrease. 

 Function of the ribs is to form a supporting and movable wall 

 for the chest, protecting the soft organs and performing a very 

 important function in respiration. 



