PRIMORDIAL CRANIUM OF THE CAT 351 



nerve makes its exit through a notch at the side of the lateral 

 mass of the atlas, between the base of the neural process poster- 

 iorly and a short but prominent atlantal process directed dorsad 

 from the lateral mass. The articular regions of the atlas and 

 occipital are comparable, in respect to their relations, to the com- 

 ponents of these two skeletal elements. In cat the occipital 

 condyles are formed at the spot where the lateral and hypochor- 

 dal arches come together, that is on the parachordal plate. This 

 is in agreement with Levi's and Weigner's observation of the 

 relation of condyle and parachordal in man. Likewise, the cor- 

 responding articular surfaces of the atlas are formed where ven- 

 tral arch and neural arch come together, namely at the massa 

 lateralis. The early establishment of similar relations to nerve 

 and articular surface offers a basis for a comparison of para- 

 chordal plate and lateral mass of atlas. Apparently these parts 

 are not distinct elements in their relation to the occipital and 

 atlantal arches, but mark a definite locus between the hypo- 

 chordal arches on the one hand, and neural or lateral occipital 

 arch on the other, constitute the region of articulation, and mark 

 the ventral limit of the exit of the nerves. In this sense the para- 

 chordal plate could not include the cartilage ventrad of the 

 notochord; this would fall into the category of the hypochordal 

 arches. The terai occipital basal plate would include the orig- 

 inally paired parachordals and the hypochordal cartilage. Com- 

 parison of parachordal plate and lateral mass which is here pro- 

 posed, while attempting to bring out the relations of the occipi- 

 tal and atlas in further detail does not at the same time close the 

 way to a better understanding of a possible relation of atlantal 

 centrum and lateral mass which has been advanced by authors 

 (Hagen, '00). 



Atlas. Reference has been made to a peculiar character of the 

 atlas, namely the foramen in the neural arch of the adult bone 

 and its relation to the notch in the arch of its cartilaginous prede- 

 cessor. This atlantal foramen transmits the vertebral artery 

 and the first spinal nerve in cat. It is present normally in most, 

 if not all mammalian orders, holding a position nearer or farther 

 from the cephahc margin of the neural arch, through which varia- 



