3 S ELEMENTARY ANATOMY. [LESS. 



(called lamince dorsales), and these meeting above form a 

 canal (the neural canal), while beneath the primitive groove 

 runs the notochord, or chorda dorsalis. 



Two other longitudinal folds (called lamina ventrales} 

 extend down one on each side from the notochord and 

 ultimately meet below. Each lamina ventralis splits longi- 

 tudinally (the split extending up towards the notochord), the 



FiGi 47. DIAGRAM OF THE DEVELOPMENT OF THE TRUNK AND ITS SKELETON 



AS SHOWN IN A SECTION OF THE TRUNK MADE AT RIGHT ANGLES TO ITS 

 LONG AXIS. 



Id, lamina dorsalis ; nc, the neural canal ; n, the notochord ; ex, cartilage ex- 

 tending dorsally and forming the foundation of the neural lamina;/^, cartilage 

 extending ventrally in lye, which represents the outer part of the split wall of 

 the ventral lamina ; Ivi, the inner part of the split wall of the ventral lamina, 

 forming by ven'.ral union with its fellow on the opposite side the alimentary 

 tube ;//, the pleuroperitoneal space between the outer and inner split walls of 

 the ventral laminae. 



inner fold of each such split uniting with its fellow of the 

 opposite side to form the alimentary canal, while the two 

 outer folds of the split form the body wall. 



Cartilage becomes deposited at intervals along each dorsal 

 lamina, and surrounds and encroaches on the notochord, so 

 that we come to have a series of cartilaginous segments 

 (representing the future vertebrae), the neural laminae of 

 which are in the dorsal folds. 



Similarly, cartilages extend down in the outer part of the 

 split wall of the ventral laminae. These are the cartilaginous 

 predecessors of the ribs, which, by their fusion in the mid- 

 ventral line, form the sternum. 



Bone is deposited in the centra (nothing of the notochord 

 being left but the pulpy substance in the middle of the inter- 

 vertebral substances), in each neural arch, in each rib, and in 

 successive portions of the sternum. 



Besides these separate ossifications there are also the 

 epiphyses, which long remain distinct as bony discs, one above 

 and one below each centrum ; and there are also epiphyses 

 in the form of little bony caps to the various processes. The 



