OSSIFICATION OF THE VERTEBRA. 19 



In the atlas, the lateral masses and posterior arches are ossified from a pair of 

 centres corresponding to those in the arches of the succeeding vertebrae. In the 

 anterior arch one or two separate nuclei appear soon after birth and even three have 

 been observed. There is frequently a small epiphysis on the posterior tubercle. 



Fig. 17. ILLUSTRATES THE OSSIFICA- 

 TION OP THE VERTEBRA. 



A, foetal vertebra, showinsr the three 

 primary centres of ossification ; 1, 2, 

 for the pedicles, laminae, and processes ; 

 3, for the body. 



B, dorsal vertebra from a child of 

 two years, as seen from above ; 1 & 2 

 are seen to have encroached upon the 

 body at *, and into the articular and 

 transverse processes, and to have united 

 behind in the spinous process, leaving 

 cartilaginous ends. 



C, dorsal vertebra at about sixteen or 

 seventeen years, showing the epipbyses 

 on the transverse processes, 4 & 5, and 

 spinous process, 6, and the upper epi- 

 physal plate of the body, 7. 



D & E, parts of a lumbar vertebra of 

 about the same age, showing, in addi- 

 tion to the foregoing, 8, the lower 

 epiphysal plate of the body; 9 & 10, 

 the epiphyses of the superior articular 

 processes (mammillary tubercles). 



Fig. 17. 



In the axis there appear, about the same time as in the other vertebrae, a pair of 

 osseous centres in the arch, one or two in the body (Cruveilhier), and shortly after- 

 wards a pair in the odontoid process which very soon unite together. At birth, the 

 odontoid process is of larger size than the body, from which it is still distinct ; and 

 its general appearance confirms the evidence of comparative anatomy, that it is to be 

 regarded as the body of the atlas. 



Fig. 18. OSSIFICATION OF THE ATLAS 



AS SEEN FROM ABOVE. 



A, the atlas before birth ; 1 & 2, ossi- 

 fied deposits in the posterior parts of the 

 arch ; the anterior part is cartilaginous. 



B, the atlas of a child in the first 

 year ; 1 & 2, as before ; 3, the point of 

 ossification in the anterior arch. 



Fig. 18. 



Fig. 18.* OSSIFICATION OF THE Axis 



AS SEEN FROM THE FRONT. 



A, the axis of the fcetus of seven 

 months, showing at 3 the centre for the 

 body, and at 4 & 5 two centres for the t 

 base of the odontoid process. 



B, the axis shortly after birth, showing 

 at 1 & 2 the centres for the arch ; 3, the 

 centre for the body ; 6, the two centres 

 of the odontoid process united into one. 



Fig. 18.* 



The sacral vertebrae present the three ordinary great centres of ossification, viz., 

 one in the body, and a pair in the arch ; but in each of the first three or sometimes 

 four sacral vertebrae the anterior part of the lateral masses on each side is formed 



c 2 



