THE VKRTEBR.E 19 



cervical sijine iiK-asures 12'") cm. (o"), the tlioracic 27 'o cm. (11"), tlic lumbar 

 17 '5 cm. (7"j, and the sacro-coccygeal portion 12-r) cm. (5"). 



Viewed in profile, the column ijresents four curves : the first, or cervical, is 

 convex anteriorly; the thoracic is much larger and longer, with its concavity for- 

 ward; the lumbar curve lias its convexity directed anteriorly, and ends somewhat 

 abruptly at the sacro-vertebral angle ; and to this succeeds the pelvic curve, 

 which corresponds to the hollow of the sacrum. In addition to these, the whcjle 

 column has a slight lateral curve with the convexity to the right, probably due to 

 nuiscular action. 



Viewed from the front, the superimposed bodies present three pyramids. The 

 first is formed by the cervical vertebrie from the second to the seventh. The bodies 

 of the lumbar and thoracic vertebnx> form a much longer pyramid. The third is 

 inverted, and formed by the sacrum and coccyx. 



Posteriorly, the colunni presents a median and two lateral rows of processes. 

 The median row is formed by the spinous "processes. In the cervical spine, with 

 the exception of the first and the seventh, they are bifid. In the thoracic set they 

 end in rounded tubercles, are long, and for the most part directed obliquely down- 

 M'ards, but in the lower part they become more horizontal until the eleventh is 

 reached. The spine of the eleventh thoracic vertebra is small and almost horizontal; 

 this is the aitti-cHnal vertebra. In the lumliar region the spinous processes are short, 



Fui. -Jl. — A Divn)ED Thokacic Vertebra. (After Turner.) 



stout plates of l)one, with their l^orders set vertically; in the sacrum they are ves- 

 tigial, and in the coccyx completely suppressed. 



The lateral rows are formed by the transverse processes, which are most marked 

 in the thoracic region, where they are rib-bearers. In the cervical spine they are 

 in the same ]:»lane as the ribs. The articular processes in the cervical region are in 

 series with tlie transverse processes of the thoracic vertel)ra}. 



Between the ridges formed by the spinous and transverse processes we recognise 

 the vertebral grooves in which muscles are lodged. The floor of each groove is 

 formed by the laminae and articular processes, with their manmiillary tubercles in 

 the lumbar and lower thoracic regions. Similar tubercles are present on the inferior 

 articular processes of the three lower cervical vertebra". The inter\'ertebral foramina, 

 oval in shape, are small in the cervical, l^ut gradually increase in size in the thoracic, 

 and arc largest in the lumbar region. 



Ossification. — The various ossific centers for the vertebra^ are deposited in the 

 cartilage which, very early in embryonic life, surrounds the notochord and gradually 

 encloses the spinal cord. 



A typical vertebra arises from three primary and numerous secondary centres. 

 The primary centres ajipear during the sixth week of embryonic life. In the 

 thoracic region the nucleus for the body is first seen, but in the cer\'ical region the 

 lateral centres make their appearance somewhat earlier. The nucleus for the body 

 is deposited around the centre, and tpiickly becomes bilol>ed. This bilobed, or 

 dumb-bell, shajjc is often so jn-onounced as to give rise to the appearance of two 



