614 JOHN D. KERNAN, JR. 



intercondyloid notch mentioned in describing the course of the 

 notochord, would be basiventrals, and the occipital arch and 

 wing would be fused basidorsals. The centra would be found 

 in the mass of connective tissue which surrounds the chorda and 

 which eventually forms the suspensory ligament of the odontoid 

 process (figs. 4 and 5). The portion of basioccipital dorsal to 

 the chorda remains to be accounted for. Examination of the 

 occipital region of early cat embryos shows that the condylar 

 portions and the hypochordal cartilage joining them ventral to 

 the chorda are formed before there is any suprachordal cartilage. 

 The chorda lies in a dorsal groove and extends craniad without 

 dorsal cartilaginous covering. In later stages cartilage forms 

 about the chorda and covers the cranial portion of the groove in 

 the basioccipital. It is this perichordal element which forms the 

 suprachordal cartilage of the basioccipital and its cranial exten- 

 sion, the clivus. It does not belong to the occipital vertebrae, 

 and its fusion to the occipital region is only owing to the intimate 

 relations of the chorda to both elements. 



There is some evidence to support this view of the occipital 

 vertebrae. First, the fact that in some lower animals (Talpa, E. 

 Fischer '01), in early stages the atlanto-occipital joint is horse- 

 shoe-shaped, partially surrounding the foramen magnum an- 

 teriorly. This articulation may better be interpreted as a joint 

 between the two anterior arches, such as occurs in birds between 

 anterior arches of atlas and axis, (it persists partly in this latter 

 vertebra), than as an articulation between vertebral body and 

 anterior arch, which it would be were the anterior edge of the 

 foramen to consist of body element. 



Second, as I have already pointed out, the relation of trans- 

 verse and costal elements are the same in respect to the lateral 

 mass of the atlas and to the condyle of the occipital cartilage 

 (fig. 2). 



Third, the manner of chondrification is much the same. As 

 described by Levi, it begins in the occipital cartilage, (figs. 8, 

 9, B), laterally, just mesial to the hypoglossal canal. These 

 centers unite ventrally, and the chondrification proceeds dorsally, 

 gradually obliterating the groove between the lateral foci. This 



