458 THE MUSCLES AND FASCIA 



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 (see 

 page 504). 



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

 two layers of fascia which are given off from the anterior or deep surface of the lum- 

 bar fascia (see page 433). It is a thin layer of fascia (part of transversalis fascia?), 

 which, passing over the anterior surface of the Quadratus lumborum, is attached, 

 internally, to the anterior surface of the transverse processes of the lumbar verte- 

 brae ; below to the ilio-lumbar 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. 288, page 435) 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 the lumbar vertebras, 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 the fascia Avhich covers its anterior 

 surface) is in relation with the colon and the kidney. Its posterior surface is in 

 relation with the middle lamella (posterior aponeurosis of the Transversalis muscle) 

 of the lumbar fascia, which separates it from the Erector spinae. The Quadratus 

 lumborum extends, however, beyond the outer border of the Erector spinae. 



Nerve-supply. The anterior branches of the lumbar nerves. 



Actions. The Quadratus lumborum draws down the last rib, and acts as a 

 muscle of inspiration ; and, at the same time, by fixing the last rib, it opposes 

 the tendency of the Diaphragm to draw it upward, and thus it becomes an assist- 

 ant to inspiration. 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. 



Muscles of the Pelvic Outlet or of the Ischio-rectal Region and Perinaeum. 



Corrugator cutis ani. Internal sphincter ani. 



External sphincter ani. Levator ani. 



Coccygeus. 

 fTransversus perinaei. TTransversus perinasi. 



r n/r i Accelerator urinae. r -n i \ Sphincter vaginas. 



In Male. < -,-, . In Female. < * v , 6 . -,. 



Erector penis. | Erector clitoridis. 



^Compressor urethrae. ^Compressor urethrae. 



The Corrugator Cutis Ani. Around the anus is a thin stratum of involuntary 

 muscular fibre, which surrounds it in a radiating manner. Internally, the fibres 

 fade off into the submucous tissue, whilst externally they blend with the true skin. 

 By its contraction it raises the skin into ridges radiating from the margin of the anus. 



The External sphincter ani is a thin, flat plane of muscular fibres, elliptical in 

 shape and intimately adherent to the integument surrounding the margin of the 

 anus. It measures about three or four inches in length from its anterior to its 

 posterior extremity, being about an inch in breadth opposite the anus. It arises 

 from the tip of the coccyx by a narrow tendinous band, and from the superficial 

 fascia in front of that bone ; and is inserted into the central tendinous point of the 

 perinaeum, joining with the Transversus perinaei, the Levator ani, and the Accelera- 

 tor urinae. Like other sphincter muscles, it consists of two planes of muscular 



