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AN INTRODUCTION TO ZOOLOGY 



spines. A foramen at the lower posterior border of the vertebral 

 neural plate and a similar one at the upper posterior border of the 

 intervertebral neural plate lead into the vertebral canal. These 

 allow for the passage of the ventral and dorsal roots of the spinal 

 nerves respectively, and from their positions it is obvious that the 

 ventral root arises in front of the corresponding dorsal root. 



FIG. 69. Vertebral column of Scy Ilium. 



I., lateral view of two vertebra? in anterior body region; LA., end-on view of vertebra in same 

 region ; II., lateral view of two vertebrae in tail region ; II. A., end-on view of tail vertebra ; 

 III., median section of two vertebrae in body region ; IV. and V., two successive stages in the 

 early development of the centrum ; adapted from Hasse. 



A., aorta ; C.C., calcined cartilage ; C.E., chorda epithelium ; E.E., membrana elastica 

 externa : E.I., membrana elastica interna ; H.A., haemal arch ; H.C., haemal canal ; H.S., haemal 

 spine ; I.L., intervertebral ligament ; I. P., intervertebral neural plate ; N., notochord ; N.C., 

 neural canal ; N.S., neural spine ; P.Pi., apertures for the exit of the dorsal and ventral roots 

 of a spinal nerve ; Per., perforations through centre of the cartilage of the centrum ; R., rib ; 

 T.P., transverse process ; V.P., vertebral neural plate. 



From the ventro-lateral edges of the centra in the middle region 

 of the body two short projections, the transverse or haemal processes, 

 project outwards. To the end of each of these is attached a fairly 

 long slender rod of cartilage, the rib, which lies laterally in the main 

 horizontal septum between the epi- and hyp-axial myotomes, and is 

 also in the planes where this septum is joined by the ordinary 



