OF THE PELVIC OUTLET. 367 



inner border of the Rectus corresponds to the linea alba, marked on the surface of the body by 

 a groove, the abdominal furrow, which extends from the infrasternal fossa to, or to a little below, 

 the umbilicus, where it gradually becomes lost. The surface of the Rectus presents three trans- 

 verse furrows, the linear transversa: The upper two of these, one opposite or a little below the 

 tip of the ensiform cartilage, and another, midway between this point and the umbilicus, are 

 usually well marked ; the third, opposite the umbilicus, is not so distinct. The umbilicus, situ- 

 ated in the linea alba, varies very much in position as regards its height. It is always situated 

 above a zone drawn round the body opposite the highest point of the crest of the ilium, gene- 

 rally being about three-quarters of an inch to an inch above this line. It generally corresponds, 

 therefore, to the fibro-cartilage between the third and fourth lumbar vertebrae. 



2. Deep Muscles of the Abdomen. 



Psoas magnus. Iliacus. 



Psoas parvus. Quadratus lumborum. 



The Psoas magnus, the Psoas parvus, and the Iliacus muscles, with the fascia 

 covering them, will be described with the Muscles of the Lower Extremity. 



The Fascia covering the Quadratus Lumborum. This is the most anterior of the 

 three layers of the lumbar fascia. It is a thin layer of fascia, which, passing over 

 the anterior surface of the Quadratus lumborum, is attached, internally, to the 

 bases of the transverse processes of the lumbar vertebrae ; below, to the ilio-lum- 

 bar ligament ; and above, to the apex and lower border of the last rib. 



The portion 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 

 ligamentum arcuatum externum. 



The Quadratus lumborum (Fig. 214, page 344) is situated in the lumbar region. 

 It is irregularly quadrilateral in shape, and broader below than above. It arises 

 by aponeurotic fibres from the ilio-lumbar ligament and the adjacent portion of the 

 crest of the ilium for about two inches, 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 four upper lumbar vertebrae. Occasionally a 

 second portion of this muscle is found situated in front of the preceding. This 

 arises from the upper borders of the transverse processes of three or four of the 

 lower lumbar vertebrae, and is inserted into the lower margin of the last rib. The 

 Quadratus lumborum is contained in a sheath formed by the anterior and middle 

 lamellae of the lumbar fasciae. 



Relations. Its anterior surface (or rather tlie fascia which covers its anterior 

 surface) is in relation with the colon, the kidney, the Psoas muscle, and the 

 Diaphragm. Between the fascia and the muscle are the last dorsal, ilio-hypogas- 

 tric, arid ilio-inguinal nerves. Its posterior surface is in relation with the middle 

 lamella of the lumbar fascia, Avhich separates it from the Ei-ector spinae. The 

 Quadratus lumborum extends, however, beyond the outer border of the Erector 

 spinae. 



Nerve-supply. The anterior branches of the last dorsal and first lumbar 

 nerves ; sometimes also a branch from the second lumbar nerve. 



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 spine 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 OF THE PELVIC OUTLET. 



The muscles of this region are situated at the pelvic outlet in the ischio-rectal 

 region and the perinaBum. They include the following: 

 I. Muscles of the ischio-rectal region. 

 II. Muscles of the perinaeum : A. In the Male ; 15. In the Female. 



