48 



OSTEOLOGY. 



Fig. 8. Development of a Vertebra. 

 By 3 primary eet/frtet 



X tfo-rBody (8$ wtcA) 



of vessels, its interior being traversed by one or two large canals for the reception 

 of veins, which converge towards a single large irregular aperture or several small 



ones at the posterior part of the body 

 of each bone. The arch and processes 

 projecting from it have, on the con- 

 trary, an exceedingly thick covering 

 of compact tissue. 



Development. Each vertebra is form- 

 ed of three primary cartilaginous por- 

 tions (fig. 8); one for each lamina and 

 its processes, and one for the body. 

 Ossification commences in the laminas 

 about the sixth week of fcetal life, in 

 the situation where the transverse pro- 

 cesses afterwards project, the ossific 

 granules shooting backwards to the 

 spine, forwards to the body, and out- 

 wards into the transverse and articular 

 processes. Ossification in the body 



f for each I a mi no, (6*- 



Fie. 9. 



/ foT etirn 

 Trail it. Proo. 

 tfyX 



2. sonutimfs / 



.pro 



Fig. 10. 



Iru 2 additional platu 



=L >'/*' 



per surface 

 ff i j J 



of lady 



wider 



uf baa 'y 



Fig. 11. Atlas. 



it res 



ffor ajiur. ancA. 



_ I for e-acA j 

 la,t.eml. matt ] 



12. Axis. 



. 

 Z far adontciJ jtroc f8* rJ 



/for ta-cJi lateral matt 



mo.) 

 Fig. 13. Lumbar Vertebra. 



2 fiaaitian/il c-c-nt rn 



for tubercles an S up. Artie. Pmc. 



makes its appearance in the middle of 

 the cartilage about the eighth week. 

 At birth, these three pieces are per- 

 fectly separate. During the first year, 

 the Iamina3 become united behind, by 

 a portion of cartilage in which the 

 spinous process is ultimately formed, 

 and thus the arch is completed. About 

 the third year, the body is joined to 

 the arch on each side, in such a man- 

 ner that the body is formed from the 

 three original centres of ossification, 

 the amount contributed by the pedicles 

 increasing in extent from below up- 

 wards. Thus the bodies of the sacral 

 vertebras are formed almost entirely 

 from the central nuclei, the bodies of 

 the lumbar segments are formed late- 

 rally and behind by the pedicles. In 

 the dorsal region the pedicles advance 

 as far forwards as the articular depres- 

 sions for the heads of the ribs, forming 

 these cavities of reception ; and in the 

 neck the whole of the lateral portions 

 of the bodies are formed by the ad- 

 vance of the pedicles. Before puberty, 

 no other changes occur excepting a 

 gradual increase in the growth of these 

 primary centres, the upper and under 

 surface of the bodies, and the ends of 

 the transverse and spinous processes, 

 being tipped with cartilage, in which 

 ossific granules are not as yet depo- 

 sited. At sixteen years (fig. 9), four 

 secondary centres appear, one for the 

 tip of each transverse process, and two 

 (sometimes united into one) for the end 

 of the spinous process. At twenty- 



