THE SPINAL COLUMN AND BACK. 149 



to) the neural canal in the 4th month, and thus the bow is 

 converted into a ring. The atlas is a permanent representative 



notochord , . , 



hypoch. bow 



body of vert. 



myotome 



■septum 



'rib 

 ^M-myotome 



jgs — hypochord. bow 

 ^s— body of vert, 

 ■septum 



hypochord. bow r . , , 



° notochord 



Fig. 118. -The development of the Membianous Basis of a Vertebra 

 A. In transverse section. B. In horizontal section showing the relation of th. 

 vertetea to the Pnrmtive Segments. The section is ULed from 'the dorsal 



of the ring thus formed. In the atlas only does the hypo-chordal 

 part of the bow become cartilaginous and subsequently ossified ; in 



neural canal 



-bow 



sheath 

 notoeh. 

 hypoch. bow 



epiph. centres 



neur. arch 



notoeh. 



centrum 



centre 

 for arch 



euro-cent, 

 sut. 



centres for body 



cavity 



costal facet 



neuro-cent sut. £ Opiate 



F. centrum 



Fig. 119. — Showing the Stages in the Development of a Vertebra. 

 A. In the Membranous Stage. B. In the Cartilaginous Stage. C. The appearance 

 of Ossific Points. D. The appearance of Secondary Ossific Centres, is 1 . The 

 epiphyseal plates of the centra. /•'. Section of an amphicoelous vertebra. 



all the other vertebrae it remains as a fibrous strand in the inter- 

 vertebral disc. 



(3) Bony Stage. — The body and bow parts of the cartilaginous 



