BACK, REGION OF THE (surgical anatomy). Under this denomination, which is of Saxon origin, it is intended to describe the posterior regions of the body situated between the head and the pelvis, including a cervical, a dorsal, and a lumbar region, varying in breadth in these different portions, and corresponding in length to that of the spine. The skeleton of this extensive region consists of the spinal column, and a portion of the ribs, and to the former of these it is chiefly indebted for its longitudinal curvatures. Thus we find it con cave in the cervical and lumbar portions, convex in the dorsal. (See SPINE.) In its whole course from the os occipitis to the base of the sacrum, we observe a central depression occasioned by the prominence of muscular masses on each side. In weak and emaciated subjects a rugged ridge takes the place of this depression ; the ridge is the series of spinous processes which have little or no muscular covering, and are hid when the mus cles on each side are much developed. At the junction of the cervical and dorsal portion, however, the ridge is scarcely ever obscured, because there the spines are very long and the muscles thin ; and again, the depression at the top of the neck is only rendered deeper by emaciation.
The length of the cervical region is well de fined by the external tuberosity of the os occi pitis above, and by the prominent spine of the last cervical vertebra below. Its breadth, at the upper part, extends from one mastoid process to the other; in the middle it becomes nar rower, and inferiorly it again spreads out almost to the acromio-clavicular articulations. Its length and breadth vary in different indi viduals. In general it is broader, propor tionally, in the male than in the female, espe cially at the upper part, where, according to Gall, it may be considered a measure of ama tiveness. At the top of this region we see a remarkable depression, called the suboccipital fossa, or cervical fossa ; its existence depends on the absence of a spinous process in the atlas, while the muscles on either side, chiefly the complexi, stand out boldly. In fat persons
a quantity of adipose substance fills up this hollow and nearly obliterates it. The upper third of the neck, and in some persons much more, is covered with hair. This part is tech nically called nucha, a term of Arabian origin. Its common appellation is nape of the neck. (See fig. 2.) The dorsal region corresponds in length to the twelve dorsal vertebrm, with their intervertebral substances, and in this dimension it is well de fined, but its breadth is not so settled ; anato mists bound it by the angles of the ribs on either side, while surgical writers extend it somewhat farther. This region is convex from above downwards, and from side to side also, if we overlook the slight central depression.
The lumbar region extends from the last dorsal vertebra to the base of the sacrum, and on each side to the outer margin of the sacro lumbalis muscle. These bounderies can gene rally be seen and felt without difficulty. It is a little concave from above downwards, convex, or nearly plane, from side to side, with the central depression slightly marked.
Integuments.—The integuments of the back are every where strong and coarse. They are particularly so over the spinous processes, where an imperfectly marked raphe exists ; they are also more fixed along that line than elsewhere, on account of the density of the cellular tissue which connects them to the su pra-spinal ligament, and in many subjects the raphb is hairy.
The sensibility of the skin is much less on the posterior than on the anterior surface of the body; the nerves and vessels are not so numerous, nor is its organization so high. Hence its resistance to the action of vesicatories and rubefacients, which must be stronger, or applied for a longer period to produce the required effect. The skin is also very unyielding, so that col lections of matter do not readily make their way to the surface, and if not opened early may spread under it extensively.