IV.] 



MAN. 



35 



its place by means of a strong transverse ligament passing 

 between the lateral masses of that bone, and separating its 

 canal into an upper or neural portion for the passage of the 

 spinal cord, and an inferior portion for the reception of the 

 odontoid process. 



The axis has posterior zygapophyses placed on the arch, 

 serially continuous with those of the rest of the vertebrae, but 

 its anterior articular facets, like those of the atlas, do not 

 belong to the arch proper, but partly to the body and partly 

 to the arch, and are therefore not exactly serially homologous 



as 



FIG. 10. Diagram showing mode of ossification of human axis (haemal or ventral 

 surface), o odontoid process, or centrum of atlas ; c proper centrum of axis ; na 

 neural arch ; as anterior articular surface ; e e e epiphyses, completing the ends of 

 the centra. 



with the zygapophyses of the other vertebrae. The trans- 

 verse processes are short, single, and perforated. The arch 

 is high, with a stout bifid spine. 



The development of the atlas and axis offers some im- 

 portant points for consideration. 



The arch of each is ossified from two centres, one on each 

 side, as in other vertebrae ; but if the axis is examined a year 

 or two after birth (Fig. 10), its body appears to be composed 

 of two parts, one placed in front of the other, the first includ- 

 ing the odontoid process and the anterior part of the body, 



D 2 



