182 Charles Russell Bardeen 



of chondrification for each of the vertebral bodies. These soon fuse 

 with one another ventral and dorsal to the chorda dorsalis. In the first 

 two vertebrae the ventral fusion takes place before the dorsal fusion. 



There are separate centers of chondrification for the neural arches. 

 In the more distal cervical vertebrge these centers are similar to those 

 of the thoracic vertebra. In the more proximal cervical vertebrae the 

 centers of chondrification appear as basal plates lateral to the anterior 

 end of the bodies of the vertebrae. With these they soon fuse. From 

 the plate-like base chondrification extends rapidly into the main part 

 of the arch. From the neural arches, laminar, articular and transverse 

 processes are developed. The costal elements have separate centers of 

 chondrification which soon fuse proximally with the bodies of the ver- 

 tebrae and distally with the tips of the transverse processes of the 

 vertebrae. The dorsal growth of the laminar processes and the forma- 

 tion of the spinous processes of the cervical vertebrae take place in the 

 main like that of the thoracic. WTien fully formed, however, the car- 

 tilaginous cervical vertebrae have essentially the shape of the adult 

 osseous cervical vertebrae. Even before the end of the second month of 

 development distinct cervical characters may be distinguished (Figs. 

 1 and 2). 



Some investigators hold that the neural arches of the mammalian 

 vertebrae contain elements of both the ventral and dorsal arches found 

 in the lower vertebrates (see Schauinsland, Hertwig's Handbuch, 1902). 

 There are theoretical grounds for believing that the ribs primitively 

 belong to the ventral arches. In the higher mammals and man, how- 

 ever, the presence of the ventral arch elements is manifest merely in 

 the caudal region, where temporary haemal processes are developed, and 

 in the upper cervical region, where, in the membranous stage, there are 

 differentiated from the ventral margins of the primitive discs bands of 

 tissue which connect the bases of the neural processes. These bands of 

 tissue have been called by Froriep the hypochordal braces (Spangen). 

 In reptiles and birds the hypochordal brace becomes converted into car- 

 tilage and connects the cartilaginous arches of each side with one 

 another. It finally becomes fused with "the ventral portion of the 

 proximal end of the vertebral body. In the primitive type of develop- 

 ment the chondrification takes place from two bilaterally placed centers, 

 each of which, according to Schauinsland, represents a ventral hemi- 

 arch. In other instances chondrification takes place from a single 

 center situated in the median line. According to Froriep, in the cow a 



