. Anatomy, descriptive and applied. Anatomy. 440 THE MUSCLES AND FASCIA Erector spinae. The Quadratus luinborum extends, however, beyond the outer border of the Erector spinae. Nerve-supply.—The anterior branches of the last thoracic and the first lumbar nerves,- sometimes also a branch from the second lumbar nerve. Actions.—The Quadratus lumborum draws down the last rib. It acts as a muscle of inspi- ration by helping to fix the origin of the Diaphragm. If the thorax and vertebral column are fixed, it may act upon the pelvis, raising it toward its own side when only one muscle is put in actio
. Anatomy, descriptive and applied. Anatomy. 440 THE MUSCLES AND FASCIA Erector spinae. The Quadratus luinborum extends, however, beyond the outer border of the Erector spinae. Nerve-supply.—The anterior branches of the last thoracic and the first lumbar nerves,- sometimes also a branch from the second lumbar nerve. Actions.—The Quadratus lumborum draws down the last rib. It acts as a muscle of inspi- ration by helping to fix the origin of the Diaphragm. If the thorax and vertebral column are fixed, it may act upon the pelvis, raising it toward its own side when only one muscle is put in action; and when both muscles act together, either from below or above, they flex the trunk. IV. MUSCLES AND FASCI.® OF THE PELVIC OUTLET. The muscles and fasciae of the pelvic outlet are those structures which form the floor of the pelvis. Perineum is a term used to designate that segment of the structure lying dorsal to the pubic arch and subpubic ligament and ventral to a line drawn transversely, in front of the anus, between the anterior part of the tuberosity of the ischium of each side. The ischiorectal space is the name given to the segment dorsal to the line above mentioned and ventral to the tip of the coccyx. This space is bounded laterally by the Gluteus maximus Fig. 331.—The perineum. The integliment and superficial layer of superficial fascia reflected. The fascia of the pelvic outlet is most easily understood if it is considered in the order of its dissection. Considered thus, it resolves itself into three strata— the superficial fascia, the triangular ligament, and the pelvic fascia. The su'per- ficial fascia is made up, as in other regions of the body, of a superficial and a deep layer. The fascia over the ischiorectal region is arranged in fatty layers, which fill the ischiorectal fossa on each side of the rectum and anus. In the region of the perineum the fascia requires fuller consideration; here it is definitely arranged into two layers—superf
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