EARLY DEVELOPMENT OF THE CERVICAL VERTEBRAE 

 AND THE BASE OF THE OCCIPITAL BONE IN MAN.^ 



BY 



ckARLES RUSSELL BARDEEN, 



University of Wisconsin. 



With 3 Figures. 



During the earlier stages of deA^elopment the cervical vertebrae re- 

 semble those of the thoracic region. The two regions soon become 

 differentiated from one another by the much greater development of the 

 costal processes of the thoracic region. The seventh cervical vertebra 

 alone, as a rule, has a large costal process, and this does not extend far 

 beyond the transverse process of the neural arch (Fig. 1). In the 

 cervical, as in the thoracic vertebrae, the development of a region of 

 loose tissue in the base of the primitive ventral process serves to 

 separate the costal element from the transverse process. In this loose 

 tissue an anastomosing artery extends from the intersegmental artery 

 on the posterior to that on the anterior side. The anastomosing artery 

 between the costal element and transverse process of the seventh cervical 

 vertebra remains small, but the more anterior anastomosing arteries give 

 rise to a large continuous vessel, the vertebral artery, which extends 

 anteriorly between the costal processes and transverse processes of the 

 root of the vertebral artery. 



In the costal processes of the seventh cervical vertebra centers of 

 chondrification are found at the period when similar centers appear in 

 the ribs. Centers of chondrification in the costal processes of the rest 

 of the cervical vertebra appear much later, usually not until the embryo 

 has reached the length of from 16-18 mm. 



As in the thoracic vertebra?, there are two bilaterally placed centers 



^The early development of the thoracic, sacral and coccygeal vertebrae has 

 previously been described in The American .Tournal of Anatomy, Vol. IV, 

 1905. 

 American Jouenal of Anatomy. — Vol. VIII. Ko. 2. 



