50 THE SKELETON. 



lower cervical vertebra, its apex being formed by the axis_or second cervical, its 

 base by the first dorsal. The second pyramid, which is inverted is formed by 

 the four upper dorsal vertebrae, the base being at the first dorsal the smaller end 

 at the fourth. The third pyramid commences at the fourth dorsal, and gradually 

 increases in size to the fifth lumbar. 



Viewed laterally (Fig. 22), the spinal column presents several curves, which 

 correspond to the different regions of the column, and are called cervical, dorsal 

 lumbar and pelvic. The cervical curve commences at the apex of the odontoid 

 process and terminates at the middle of the second dorsal vertebra; it is convex 

 in front, and is the least marked of all the curves. The dorsal curve, which is 

 concave forward, commences at the middle of the second, and terminates at the 

 middle of the twelfth dorsal. Its most prominent point behind corresponds to 

 the spine of the seventh dorsal vertebra. The lumbar curve commences at the 

 middle of the last dorsal vertebra, and terminates at the sacro-vertebral angle. 

 It is convex anteriorly ; the convexity of the lower three vertebrae being much 

 greater than that of the upper two. The pelvic curve commences at the sacro- 

 vertebral articulation and terminates at the point of the coccyx. It is concave 

 anteriorly. The dorsal and pelvic curves are the primary curves, and begin to 

 be formed at an early period of foetal life, and are due to the shape of the bodies 

 of the vertebrse. The cervical and lumbar curves are compensatory or secondary, 

 and are developed after birth in order to maintain the erect position. They are 

 due mainly to the shape of the intervertebral disks. 



The spine has also a slight lateral curvature, the convexity of which is 

 directed toward the right side. This is most probably produced, as Bichat first 

 explained, chiefly by muscular action, most persons using the right arm in prefer- 

 ence to the left, especially in making long-continued efforts, when the body is 

 curved to the right side. In support of this explanation it has been found by 

 Beclard that in one or two individuals who were left-handed the lateral curvature 

 was directed to the left side. 



The movable part of the spinal column presents for examination an an- 

 terior, a posterior, and two lateral surfaces ; a base, a summit, and spinal 

 canal. 



The anterior surface presents the bodies of the vertebrae separated in the 

 recent state by the intervertebral disks. The bodies are broad in the cervical 

 region, narrow in the upper part of the dorsal, and broadest in the lumbar region 

 The whole of this surface is convex transversely, concave from above downward in 

 the dorsal region, and convex in the same direction in the cervical and lumbar 

 regions. 



The posterior surface presents in the median line the spinous processes. These 

 are short, horizontal, with bifid extremities, in the cervical region. In the dorsal 

 region they are directed obliquely above, assume almost a vertical direction in the 

 middle, and are horizontal below, as are also the spines of the lumbar vertebrae. 

 They are separated by considerable intervals in the loins, by narrower intervals 

 in the neck, and are closely approximated in the middle of the dorsal region. 

 Occasionally one of these processes deviates a little from the median line a fact 

 to be remembered in practice, as irregularities of this sort are attendant also on 

 fractures or displacements of the spine. On either side of the spinous processes, 

 extending the whole length of the column, is the vertebral groove formed by the 

 laminae in the cervical and lumbar regions, where it is shallow, and by the laminae 

 and transverse processes in the dorsal region, where it is deep and broad. In 

 the recent state these grooves lodge the deep muscles of the back. External to 

 the vertebral grooves are the articular processes, and still more externally the 

 transverse process. In the dorsal region the latter processes stand backward, on 

 a plane considerably posterior to the same processes in the cervical and lumbar 

 regions. In the cervical region the transverse processes are placed in front of the 

 articular processes, and on the outer side of the pedicles, between the interver- 



