162 THE SKELETON. 



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- 

 tebral foramina. In the dorsal region they are posterior to the pedicles, interver- 

 tebral foramina, and articular processes. In the lumbar they are placed also in 

 front of the articular processes, but behind the intervertebral foramina. 



The lateral surfaces are separated from the posterior by the articular processes 

 in the cervical and lumbar regions, and by the transverse processes in the dorsal. 

 These surfaces present in front the sides of the bodies of the vertebrae, marked in 

 the dorsal region by the facets for articulation with the heads of the ribs. More 

 posteriorly are the intervertebral foramina, formed by the juxtaposition of the 

 intervertebral notches, oval in shape, smallest in the cervical and upper part of 

 the dorsal regions, and gradually increasing in size to the last lumbar. They are 

 situated between the transverse processes in the neck, and in front of them in the 

 back and loins, and transmit the spinal nerves. 



The base of that portion of the vertebral column formed by the twenty-four 

 movable vertebrae is formed by the under surface of the body of the fifth lumbar 

 vertebra ; and the summit by the upper surface of the atlas. 



The vertebral or spinal canal follows the different curves of the spine ; it is 

 largest in those regions in which the spine enjoys the greatest freedom of move- 

 ment, as in the neck and loins, where it is wide and triangular ; and narrow and 

 rounded in the back, where motion is more limited. 



Surface Form. The only part of the vertebral column which lies closely under the skin, 

 and so directly influences surface form, is the apices of the spinous processes. These are always 

 distinguishable at the bottom of a median furrow, which, more or less evident, runs down the 

 mesial line of the back from the external occipital protuberance above to the middle of the 

 sacrum below. In the neck the furrow is broad, and terminates below in a conspicuous projec- 

 tion, which is caused by the spinous process of the seventh cervical vertebra (vertebra prorui- 

 nens). Above this the spinous process of the sixth cervical vertebra may sometimes be seen; 

 the other cervical spines are sunken, and are not visible, though the spine of the axis can be 

 felt, and generally also the spines of the third, fourth, and fifth cervical vertebrae. In the 

 dorsal region the furrow is shallow, and during stooping disappears, and then the spinous pro- 

 cesses become more or less visible. The markings produced by these spines are small and close 

 together. In the lumbar region the furrow is deep, and the situation of the lumbar spines is 

 frequently indicated by little pits or depressions, especially if the muscles in the loins are well 

 developed and the spine incurved. They are much larger and farther apart than in the dorsal 

 region. In the sacral region the furrow is shallower, presenting a flattened area which terminates 

 below at the most prominent part of the posterior surface of the sacrum, formed by the spinous 

 process of the third sacral vertebra. At the bottom of the furrow may be felt the irregular 

 posterior surface of the bone. Below this, in the deep groove leading to the anus, the coccyx 

 may be felt. The only other portions of the vertebral column which can be felt from the surface 

 are the transverse processes of three of the cervical vertebrae viz. the first, the sixth, and the 

 seventh. The transverse process of the atlas can be felt as a rounded nodule of bone just below 

 and in front of the apex of the mastoid process, along the anterior border of the sterno-mastoid. 

 The transverse process of the sixth cervical vertebra is of surgical importance. If deep pressure 

 be made in the neck in the course of the carotid artery, opposite the cricoid cartilage, the 

 prominent anterior tubercle of the transverse process of the sixth cervical vertebra can be felt. 

 This has been named Chassaignacs tubercle, and against it the carotid artery may be most 

 conveniently compressed by the finger. The transverse process of the seventh cervical vertebra 

 can also often be felt. Occasionally the anterior root, or costal process, is large and segmented 

 off, forming a cervical rib. 



Surgical Anatomy. Occasionally the coalescence of the laminse is not completed, and con- 

 sequently a cleft is left in the arches of the vertebrae, through which a protrusion of the spinal 

 membranes (dura mater and arachnoid), and sometimes of the spinal cord itself, takes place, 

 constituting the disease known SLSspina bifida. This disease is most common in the lumbo-sacral 

 region, on account of the fact, previously stated, that the closure of the arches takes place 

 gradually from above downward ; but it may occur in the dorsal or cervical region, or the arches 

 throughout the whole length of the canal may remain unapproximated. In some rare cases, in 

 consequence of the non-coalescence of the two primary centres from which the body is formed, 

 a similar condition may occur in front of the canal, the bodies of the vertebrae being found cleft 

 and the tumor projecting into the thorax, abdomen, or pelvis, between the lateral halves of the 

 bodies affected. 



The construction of the spinal column of a number of pieces, securely connected together 

 and enjoying only a slight degree of movement between any two individual pieces, though per- 



