OSSIFICATION OF THE VERTEBRJE. 



19 



becomes greater as far as the first dorsal 

 vertebra," thence it is again gradually 

 contracted as far as the last dorsal, and 

 becomes suddenly much greater in the 

 lumbar region. 



In a lateral view the antero -posterior 

 diameter of the bodies increases in 

 descending through the dorsal and 

 lumbar regions. 



Viewed from behind the spines 

 occupy the middle line. On each side 

 are the vertebral grooves, corresponding 

 to the laminaj, and bounded externally 

 in the cervical and dorsal regions 

 by the transverse processes, and iu 

 the lumbar by the mammillary pro- 

 cesses. Along each groove is a series 

 of spaces between the laminse, which, 

 in the natural condition, are filled 

 up by the yellow ligaments. The 

 extent of these intervals is very trifling 

 in the neck and in the greater part 

 of the back ; it increases in the lower 

 third of the dorsal, and still more in 

 the lumbar region. The interval be- 

 tween the occipital bone and the arch 

 of the atlas is consideral^le, and so is 

 that between the last lumbar vertebra 

 and the sacrum. 



Fig. 16. — The Vertebral Column viewed from 

 THE Left Side. (A. T.) \ 



The letters and numbers indicate the several 

 vertehrre. The antero-posterior curvatures of 

 the column are shown, together with the shape 

 and size of the bodies and intervertebral spaces, 

 the form and transitions of the transverse and 

 spinous processes, and the diiferences in the 

 costal articulating surfaces. 



Fiff. 16. 



\-4j9 



J^i 



OSSIFICATION OF THE VERTEBBiE. 



The "Vertebrae in general. — The ossifi- 

 cation of each vertebra proceeds in cartilage 

 from three princii^al centres, one for the 

 main part of the body, and one on each 

 side for the arch and processes, together 

 with a part on each side of the body. The 

 lateral centres appear about the 7th week, 

 that of the body very soon afterwards. From 

 these centres the ossification extends gradu- 

 ally outwards, so as at last to form the greater 

 part of the vertebra. That of the body does 

 not pass, however, in the dorsal vertebrae, 

 the place of articulation of the head of the 

 rib, leaving on each side a portion of the 

 body which is formed from the lateral centre, 



SI 



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