132 



THE SKELETON. 



Fi<?. 88. Lateral View of the Spine. 



lit Cervical 

 or Atlas 



3d Cervical 

 or Axis. 



7-1 



1-1 



4- 



ff-\ 



7- 



S-\ 



.9 



second pyramid, which is inverted, is formed 

 by the four upper dorsal vertebras, the base 

 being at the first dorsal, the smaller end at the 

 fourth. The third pyramid commences at the 

 fourth dorsal, and gradually increases in size 

 to the fifth lumbar. 



Viewed laterally (Fig. 88), the spinal column 

 presents several curves, which correspond to the 

 different regions of the column, and are called 

 cervical, dorsal, lumbar, and pelvic. The cer- 

 vical curve commences at the apex of the odon- 

 toid process, and terminates at the middle of the 

 second dorsal vertebra ; it is convex in front, 

 and is the least marked of all the curves. The 

 dorsal curve, which is concave forwards, com- 

 mences at the middle of the second, and ter- 

 minates at the middle of the twelfth dorsal. 

 Its most prominent point behind corresponds 

 to the body of the seventh or eighth vertebra. 

 The lumbar curve commences at the middle 

 of the last dorsal vertebra, and terminates at 

 the sacro- vertebral angle. It is convex ante- 

 riorly ; the convexity of the lower three ver- 

 tebra being much greater than that of the 

 upper ones. The pelvic curve commences at 

 the sacro-vertebral articulation, and terminates 

 at the point of the coccyx. It is concave an- 

 teriorly. These curves are partly due to the 

 shape of the bodies of the vertebrae, and partly 

 to the intervertebral substances, as will be 

 explained in the Articulations of the Spine. 



The spine has also a slight lateral curva- 

 ture, the convexity of which is directed to- 

 ward the right side. This is most probably 

 produced, as Bichat first explained, chiefly 

 by muscular action ; most persons using the 

 right arm in preference to the left, especially 

 in making long-continued efforts, when the 

 body is curved to the right side. In support 

 of this explanation, it has been found, by Bd- 

 clard, that in one or two individuals who were 

 left-handed, the lateral curvature was directed 

 to the left side. 



The spinal column presents for examina- 

 tion an anterior, a posterior, and two lateral 

 surfaces; a base, summit, and vertebral canal. 



The anterior surface present the bodies of 

 the vertebras separated in the recent state by 

 the intervertebral disks. The bodies are broad 

 in the cervical region, narrow in the upper 

 part of the dorsal, and broadest in the lumbar 

 region. The whole of this surface is convex 

 transversely, concave from above downwards 

 in the dorsal region, and convex in the same 

 direction in the cervical and lumbar regions. 



The posterior surface presents in the median 

 line the spinous processes. These are short, 



