28 



A MANUAL OF ANATOMY 



about the seventh week of intra-uterine life at the junction of the pedicles and 

 laminae, and from these ossification invades the neural arch, with its processes, 

 and the adjacent portions of the body. The centre for the principal part of 

 the body appears about the eighth week in the portion of cartilage dorsal to 



B 



Appears about the 8th Week 



Appears about the 7th 



Week of 



intra-uterine 



Hfe 



Neural Arch 



Neural Arch 



Fig. 18. — Ossification of the True VERTEBRi^. 



A, Cervical Vertebra at the Third Month ; B, Cervical Vertebra at Birth ; 

 C, Thoracic Vertebra at Birth. 



the notochord. It is usually single at first, but it soon assumes a bilobed 

 form, and so it comes to surround the notochord, which becomes constricted, 

 and ultimately disappears. This nucleus may be double, and, if this character 

 persists, the body ossifies in two separate parts, or, if one nucleus should be 



Appears about the i6th, and 

 joins about the 25th, Year 



Transverse Epiphysis 

 (i6th and 25th Ye.nr) 



Mammillary Epiphysis 

 (i6th and 25th Year) 



Spinous Epiphysis 

 - • ■ ;th -• • 



(i6th and 25th Year) 



Fig. 19. — Lumbar Vertebra, showing the Epiphyses. 

 A, The Body ; B. The Neural Arch. 



arrested, only one-half of the body ossifies (Turner). At birth a vertebra is 

 composed of three osseous parts, connected by cartilage, namely, the principal 

 part of the body, and the two halves of the neural arch, each bearing a small 

 portion of the body. The lamina; unite behind in the first year, except in the 



