12 THE BONES. 



The Spine in General. 



The vertebral column has now to be considered in its entirety, and examined 

 successively in its superior face, its inferior face, its lateral faces, and its spinal 

 canal. Afterwards its direction and mobility will be noticed. 



Superior surface. — This presents, on its median line, the series of spinous pro- 

 cesses. But little salient in the cervical region, these eminences are much 

 developed in the dorsal and lumbar, where they constitute a long crest — the 

 dorso-Iumbar spine, as well as in the sacrum, where they form the sacral spine. 

 They soon disappear in the coccygeal vertebrae. Outwards, and on each side of 

 these processes, is seen a succession of tubercles for insertion, represented iu the 

 cervical and lumbar vertebrae by articular processes, and in the dorsal vertebrae 

 by the superior or rugose portion of the transverse processes. These tubercles 

 are disposed in line, and separated from the spinous processes by a channel 

 designated the vertebral groove, which is more or less deep and wide. It is on 

 these, and on the spinous processes, that the extensor muscular fascicuU of the 

 spine receive the greater portion of their fixed or movable insertions. 



Inferior surface. — Wide at the neck, this surface becomes narrow in the dorsal 

 region, to be again widened at the lumbo-sacral region, and once more contracted 

 at the coccyx. Crests more or less developed, which divide the vertebral bodies 

 into two lateral portions, right and left, are remarked. 



Lateral surfaces. — These offer for study the thirty-six intervertebral foramina, 

 through which the spinal nerves pass. They exhibit besides, in the neck, the 

 transverse processes ; in the back, the external facets of these processes, and the 

 intervertebral facets, all destined to sustain the heads of the ribs ; on the loins, 

 the transverse or costiform processes. It may be remarked that the ribs and the 

 transverse processes of the neck and loins furnish points of insertion to the 

 powerful muscles which produce the lateral movements of the spine. In the sacrum, 

 the lateral faces are formed for the articulation of the spine with the ossa 

 innominata. 



Spinal canal. — This canal communicates, in front, with the cranial cavity. 

 Very wide in the atlas, for the reception of the odontoid process and to permit 

 the rotatory movements of the head without injury to the spinal cord, this canal 

 suddenly diminishes in the axis. It again dilates at the termination of the 

 cervical region and the commencement of the dorsal ; there the spinal cord 

 presents a greater volume, and the movements of the spine are very extensive. 

 Towards the middle of the back, the spinal canal offers its smallest diameter ; it 

 widens from this part to the lumbo-sacral articulation ; after which it contracts 

 rapidly, and disappears altogether near the fourth or fifth coccygeal vertebra. 

 The lumbo-sacral dilatation coincides with the enlargement of the cord in this 

 region, and with the enormous quantity of nerves lying beside it. 



Direction of the Spine.— The spine does not extend in a straight line from the 

 head to the posterior extremity of the body. If it is followed from the caudal 

 extremity — which is free and looks downwards — to the anterior extremity, it will 

 be observed that it passes upwards and forwards, forming a convex inflexion 

 corresponding to the roof of the pelvis. In the lumbar and posterior half of the 

 dorsal region, it is nearly horizontal and rectilinear ; thence it descends to the 

 cervical region, where it again rises and forms two curves — one, posterior, bend- 

 ing upwards, the other anterior, passing downwards. This direction "of the spine 

 gives it the form of a console. 



