Charles E. Bardeen 275 



the second, alone give rise to cartilagenous plates. From these only 

 pediclar and incomplete articnlar and transverse processes* arise. The 

 cornua of the adult coccyx represent fairly well the form of the early 

 nenral semi-arches. The transverse processes develop in close connection 

 with the costal processes. 



In the thoracic vertebrae cartilagenous ribs develop from separate 

 centers in the blastemal costal processes. 



In the lumbar vertebrse separate cartilagenous centers probably always 

 arise in these processes, but they are developed later than those of the 

 thoracic vertebrse and quickly become fused with the cartilage of the 

 transverse processes. The transverse processes of the adult lumbar ver- 

 tebrse represent at the base a fusion of embryonic cartilagenous costal 

 and transverse processes, but in the blade an ossification of membranous 

 costal processes. 



In the sacral vertebrse separate cartilagenous costal centers are de- 

 veloped but they soon become fused at the base with the transverse 

 processes of the neural plates. Laterally by fusion of their extremities 

 the costal processes give rise to an auricular plate for articulation with 

 the ilium. 



In the coccygeal vertebrse the costal processes of the first become fused 

 with the transverse processes and develop into the transverse processes 

 of the adult coccyx. I have been unable definitely to determine whether 

 a separate costal cartilage is developed in these processes or cartilage 

 extends into them from the neural processes. The costal processes of 

 the other coccygeal vertebrse have merely a very transitory blastemal 

 existence. 



For a brief period the more distal sacral and the coccygeal vertebrse 

 have membranous hsemal processes. 



Centers of ossification correspond in general with centers of chondro- 

 fication, but, as in the case of the vertebral bodies and the more distal 

 sacral neuro-costal processes, a single center of ossification may represent 

 two centers of chondrofication. 



B. 



THE CURVES AND THE PROPORTIONATE REGIONAL LENGTHS OF 



THE SPINAL COLUMN DURING THE FIRST THREE MONTHS 



OF EMBRYONIC DEVELOPMENT. 



In 1879 Aeby contributed an imoprtant paper dealing with the lengtli 

 of the various regions of the spinal column at different ages, the heigh. t 

 of the constituent vertebrse and the thickness of the intervertebral disks 



