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Henry Gray (1825–1861).  Anatomy of the Human Body.  1918.
 
to the iliolumbar ligament; above, to the apex and lower border of the last rib. The upper margin of this fascia, which extends from the transverse process of the first lumbar vertebra to the apex and lower border of the last rib, constitutes the lateral lumbocostal arch (page 405). Laterally, it blends with the lumbodorsal fascia, the anterior layer of which intervenes between the Quadratus lumborum and the Sacrospinalis.
  The Quadratus lumborum (Fig. 389, page 398) is irregularly quadrilateral in shape, and broader below than above. It arises by aponeurotic fibers from the iliolumbar ligament and the adjacent portion of the iliac crest for about 5 cm., and is inserted into the lower border of the last rib for about half its length, and by four small tendons into the apices of the transverse processes of the upper four lumbar vertebræ. Occasionally a second portion of this muscle is found in front of the preceding. It arises from the upper borders of the transverse processes of the lower three or four lumbar vertebræ, and is inserted into the lower margin of the last rib. In front of the Quadratus lumborum are the colon, the kidney, the Psoas major and minor, and the diaphragm; between the fascia and the muscle are the twelfth thoracic, ilioinguinal, and iliohypogastric nerves.

Variations.—The number of attachments to the vertebræ and the extent of its attachment to the last rib vary.

Nerve Supply.—The twelfth thoracic and first and second lumbar nerves supply this muscle.

Actions.—The Quadratus lumborum draws down the last rib, and acts as a muscle of inspiration 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.
 
6e. The Muscles and Fasciæ of the Pelvis
 
Obturator internus.
Levator ani.
Piriformis.
Coccygeus.
  The muscles within the pelvis may be divided into two groups: (1) the Obturator internus and the Piriformis, which are muscles of the lower extremity, and will be described with these (pages 476 and 477); (2) the Levator ani and the Coccygeus, which together form the pelvic diaphragm and are associated with the pelvic viscera. The classification of the two groups under a common heading is convenient in connection with the fasciæ investing the muscles. These fasciæ are closely related to one another and to the deep fascia of the perineum, and in addition have special connections with the fibrous coverings of the pelvic viscera; it is customary therefore to describe them together under the term pelvic fascia.

Pelvic Fascia.—The fascia of the pelvis may be resolved into: (a) the fascial sheaths of the Obturator internus, Piriformis, and pelvic diaphragm; (b) the fascia associated with the pelvic viscera.
  The fascia of the Obturator internus covers the pelvic surface of, and is attached around the margin of the origin of, the muscle. Above, it is loosely connected to the back part of the arcuate line, and here it is continuous with the iliac fascia. In front of this, as it follows the line of origin of the Obturator internus, it gradually separates from the iliac fascia and the continuity between the two is retained only through the periosteum. It arches beneath the obturator vessels and nerve, completing the obturator canal, and at the front of the pelvis is attached to the back of the superior ramus of the pubis. Below, the obturator fascia is attached to the falciform process of the sacrotuberous ligament and to the pubic arch, where it becomes continuous with the superior fascia of the urogenital diaphragm. Behind, it is prolonged into the gluteal region.
  The internal pudendal vessels and pudendal nerve cross the pelvic surface of

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