6o 



ELEMENTS OF MAMMALIAN ANATOMY. 



rudiment of a rib. The transverse process of the fifth ends 



nl 



FIG. 24. LATERAL ASPECT OF THE Axis. 



ar st, Anterior zygapophyses ; od pr, odontoid process ; nl sp, neural spine 

 or spinous process; p zg, posterior zygapophysis ; trs pr, transverse 

 process; vrt c, vertebrarterial canal. 



in three branches. The following features are common to 



all thirteen thoracic vertebrae : a 

 spinous process, projecting from 

 the dorsum of the neural arch ; 

 two cephalic articular processes or 

 anterior zygapophyses, facing 

 dorsad or dorsolaterad ; two cau- 

 dal articular processes or posterior 

 zygapophyses, facing ventrad or 

 ventromesad; a body whose 

 transverse diameter is greater 

 than the vertical diameter; and 

 transverse processes. There are 

 two half facets on each side of 

 the body of every thoracic verte- 

 bra except the first, eleventh, 

 twelfth, and thirteenth. The 

 head of a rib thus articulates 

 with two vertebrae (Fig. 28). 

 The body of the first vertebra 



bears on each side a whole facet and a half facet. The 



ce n 



FIG. 25. - - LATEROCAUDAL 

 ASPECT OF THE SECOND 

 THORACIC VERTEBRA. 



tr, Transverse process; nc, 

 neural canal; ce, facet for 

 tubercle of rib ; ar, poste- 

 rior zygapophysis; s, spi- 

 nous process ; c, centrum ; 

 n, intervertebral notch ; e, 

 pedicle; /, lamina. 



