348 ROBERT J. TERRY 



paired anlagen of the atlantal centrum were noted. Evidence 

 of the beginning of the occipital centrum was presented in an 

 embryo of 14.5 mm.; the anlage was clearly defined in a later 

 stage (15.3 mm.) as a pair of centers behind the notochord, which 

 pass in a caudal direction gradually into the older centers of the 

 body of the atlas. In man, according to Weigner, the body of 

 the definitive epistropheus with its tooth-process, is developed 

 from three vertebral bodies; those of the occipital vertebra, atlas 

 and epistropheus. The dens itself is formed from the centrum 

 of the occipital vertebra and of the atlas. In the present work 

 no separate centers, in advance of that for the atlantal cen- 

 trum, were seen, but the tissue about the occipital notochord 

 became condensed next to the chondrifying center of the atlas, 

 and eventually became the cartilaginous apex of the dens 

 epistrophei. In the ossification of the dens epistrophei of cat 

 (as in several mammals) there is, in addition to the bilateral 

 atlantal centers, a single center for the apex of this process 

 (Jayne '98). 



Since Froriep's work on the development of the occipital 

 region ('83, '86, '02), the interpretation which that investigator 

 drew from his own results of the relation between cranial and 

 vertebral development and structure has been, in general, sus- 

 tained; some of the conclusions have, however, been modified 

 by new evidence brought out by recent research. Noordenbos, 

 in 1905, attacked the evidence which has been used in support 

 of the vertebral theory of the skull, claiming in effect that it 

 does not support the homology of parachordal plate and occipital 

 arches with vertebral centra and vertebral arches. Noordenbos 

 rightly objects to the comparison of vertebral bodies, arising as 

 separate, rounded cartilaginous masses, with the parachordal 

 plates, continuous unsegmented masses presenting no trace of 

 special chondral centers. He states that vertebrae arise around 

 the body notochord while the parachordal plate does not. This 

 plate takes origin in one of the three ways mentioned above: 

 as an independent center at the side of the notochord; in con- 

 nection with the lateral occipital arch ; in connection with a 

 hypochordal plate. By the van Wijhe method the vertebral 



