VBETEBRAL COLUMN 115 



LATERAL ASPECT. 



When viewed from the side, it will be seen that the vertebral 

 column is not straight, but curved in the dorso-ventral plane, the 

 degree of curvature of course varying with the movements of the 

 animal. In the position assumed in Avalking, the column traces but 

 two curves. The first curve extends from the cephalic end to the 

 tenth thoracic vertebra, and its convexity faces ventrally. The 

 second curve begins at the tenth thoracic and ceases at the cephalic 

 end of the sacrum, and its concavity is ventral. The sacrum and 

 first caudal vertebra describe a curve whereof the concavity is ventral, 

 but the tip of the tail is usually somewhat elevated, which causes a 

 fourth curve in the reverse direction from the preceding two. 



The lateral aspect of the column shows (1) the length and direction 

 of the spinous processes, (2) the dorso-ventral height of the pedicles 

 and laminae, (3) the diameter of the intervertebral foramina, (4) the 

 point of origin of the transverse processes, and (5) the dorso-ventral 

 height of the bodies of the constituent vertebras. 



(1) The spinous process is absent in the atlas, very large in the 

 axis, rudimentary in the third vertebra, and then increases in length 

 to the cephalic thoracic region, where the length remains the same 

 for several vertebrae ; it then diminishes to the tenth thoracic, which 

 has the shortest spine of all the trunk vertebrae. From the eleventh 

 the spines gradually increase in length to the end of the lumbar 

 region. They are shorter again in the sacrum and absent in the 

 caudal vertebrae. The fourth, fifth, and sixth cervical spinous pro- 

 cesses point dorsally and toward the head, and the seventh cervical 

 and first few thoracic almost directly dorsally ; in the remaining 

 thoracics as far as the tenth the spinous processes are directed toward 

 the tail as well as dorsally. The eleventh, the anticlinal, spinous pro- 

 cess points dorsally, and marks the point where the two curves of 

 the column join. The remaining spinous processes are directed toward 

 the head as well as dorsally. The tips of the spinous processes are 

 acute in the cervical and thoracic regions, except where elongated in 

 the second cervical, swollen and rounded in the first and second 

 thoracic, and truncated and elongated from head to tail in the twelfth 

 and thirteenth thoracic, a condition which obtains in all the lumbar 

 vertebrae except the last. 



(2) The pedicles have a great dorso-ventral diameter in the 



