807 



apophysial one : they are equal in the Chimpanzee : the arterial foramina are relatively larger 

 and the posterior zygapophyses are relatively much larger than in the Chimpanzee. 



These differences chiefly relate to the more secure articulation and support of the vertically 

 sustained head, and to the larger size of the cerebral organ in part nourished by the vertebral 

 arteries, in the Human species. The development of the zygapophyses gives a greater antero- 

 posterior extent to those parts of the atlas, and the transverse processes are thicker in pro- 

 portion to their length. 



5187. The axis. 



The lower surface of the centrum is less flattened than in the Chimpanzee, the middle line 

 being produced almost into a ridge. The transverse process is thicker and more obtuse in 

 proportion to its length : both the anterior and posterior zygapophyses are relatively larger : 

 the neural canal is relatively wider transversely : the neural spine is much less developed : in 

 fact, what is usually described as the bifurcated spine of the axis seems rather to be the upper 

 slightly produced extremities of the not completely coalesced neurapophyses of that vertebra 

 hi Man. 



Lines drawn parallel with the transverse plane of the anterior zygapophyses would meet at 

 a right angle in the Chimpanzee, but at a more open angle in Man, especially in the White 

 races. 



5188. The third cervical vertebra. 



The anterior angle of the base of each neurapophysis is produced forwards beyond the 

 centrum, and assists in forming, but in a less proportion than in the Chimpanzee, the trans- 

 verse concavity for the backwardly produced body of the axis. The centrum is larger in 

 proportion to the rest of the vertebrae than hi the Chimpanzee, save in its antero-posterior 

 dimension. The pleurapophysial part of the transverse process forms a distinct obtuse angle 

 from the diapophysial part, which is shorter, thicker, and more obtuse than hi the Chim- 

 panzee. The same difference is here repeated hi the greater relative size of the zygapophyses, 

 particularly the anterior ones. The transverse diameter of the neural canal is relatively 

 greater. The neural spine is much shorter and thicker. 



5189. The fourth cervical vertebra. 



The sides of the anterior concavity are still formed by the neurapophyses, which are less 

 produced than hi the preceding vertebrae, or than in the corresponding vertebrae of the Chim- 

 panzee. The diapophyses and neural spine are shorter than hi the Chimpanzee, especially 

 the latter. The zygapophyses are relatively larger. The pleurapophysial and diapophysial 

 parts of the transverse process are nearly equally developed, and are bent forwards on the 

 sides of the groove which impresses the fore part of the transverse process. The pleurapo- 

 physial boundary for the canal for the vertebral artery is here much thinner than the diapo- 

 physial one. 



