128 ANATOMY OF THE WOOD RAT 



vertebra. As far caudad as the ninth (inclusive), or in two 

 Homodontomys the tenth, thoracic vertebra the spines are 

 relatively slender, and show a definite inclination caudad. 

 Posterior to this, the remaining thoracic spines are of the 

 lumbar t^^pe, being very broad in a sagittal direction. In 

 man there is a somewhat similar change in the shape of the 

 spines posterior to the tenth thoracic vertebra, and pos- 

 terior to the ninth in the cat, although the tenth and eleventh 

 are intermediate in form. The point upon the vertebral 

 column at which the inclination of the spines changes in- 

 dicates the center of motion and seems to be influenced 

 chiefly by the spinalis dorsi, although other factors are un- 

 doubtedly involved to some extent. 



The thoracic vertebrae as far caudad as the tenth (in- 

 clusive) have single, lateral processes on either side above 

 the ribs, which may be termed transverse processes solely by 

 reason of their general position, although I am not aware 

 that their precise homology with what are herein termed 

 the transverse processes of the cervical series has ever been 

 established in a thoroughly satisfactory manner. Each 

 vertebra has also a pair of postzygapophyses, but in the 

 first nine of this series these are hardly developed as true 

 processes. 



The transverse processes of the tenth thoracic are broader 

 in a sagittal direction, while in the eleventh, these have sep- 

 arated to form the met- and anapophyses (see fig. 27) . The 

 former, in this vertebra, are situated more dorsad than the 

 transverse processes of the tenth. Progressively caudad, 

 each of the processes thereafter increases in size. The post- 

 zygapophyses, beginning with the tenth thoracic, also in- 

 crease progressively in size in ratio with the metapophyses. 

 The eleventh thoracic is the narrowest of all the body 

 vertebrae, and each one succeedingly caudad is a trifle 

 broader. 



