CHONDROCRANIUM OF A 20 MM. HUMAN EMBRYO 613 



ing on the foramen magnum. He represented everything mesiad 

 to a line drawn from the cranial tip of the jugular foramen to the 

 ventral foraminal prominence as containing body elements. 

 The outer part of the condyle he took to be the inferior articulaf 

 process, the jugular tubercle the superior articular process; the 

 paracondyloid process, the transverse and costal elements; and 

 the thick area bordering the foramen magnum, the neural arch, all 

 belonging to the occipital vertebrae. The neural arch elements 

 of the unsegmented vertebrae he said fused with that of the 

 occipital vertebra, to form the occipital wing, and their pedicles 

 all fused into the comparatively small bar of cartilage cranial to 

 the hypoglossal canal. 



There are some objections to this analysis. The jugular 

 tubercle belongs to the structures craniad of the hypoglossal 

 canal. Hence it cannot very well be the superior articular 

 process of the occipital vertebra (fig. 1). 



The condyle (fig. 2) cannot be an inferior articular process as 

 found in the cervical vertebrae, since its relations to surrounding 

 structures are fundamentally different. Thus, the condyle is 

 ventral to the transverse process of the occipital vertebra, ven- 

 tral to the transverse plane through the notochord, and ventral 

 to the suboccipital nerve, whereas the articular processes of the 

 cervical vertebrae are dorsal to these structures (fig. 2). 



The condyle has the same relations to the transverse and costal 

 processes of the occipital vertebra and to the chorda as has the 

 lateral mass of the atlas to its transverse and costal processes. As 

 shown by H. Gadow ('96), the atlas may be analyzed as follows: 

 the lateral mass is formed by the fusion of basiventral and basi- 

 dorsal elements where they meet at the side of the chorda. The 

 basiventral elements, here retained, form the ventral arch of the 

 atlas. The basidorsal elements, form the neural arch of the atlas. 

 The centrum fuses with that of the axis to form the dens epis- 

 trophei. 



It is possible that the occipital vertebrae are vertebrae of the 

 atlas type. Then the condyles and the tissue immediately 

 dorsal would be formed by fusion at the junction of basiventral 

 and basidorsal elements; the hypochordal elements bordering the 



