OBLIQUUS LXTERXCS— ('REMASTER 401 



and ill its upper three-fourths it divides into an anterior and a posterior Y>lane wliieh 

 together form the sheath of the rectus muscle. In the lower fourth of the al)dt)men 

 the wliole of the aponeurosis passes in front of this muscle. The line of division of 

 the a])oneurosis of the internal ol)li(|ue is indicated on the surface of the abdomen 

 l)y a furrow called the linea semilunaris, which lies between the fleshy part of the 

 muscle and the outer border of the rectus muscle, and forms a curve, concave 

 inwards, which extends from the cartilage of the ninth rib alcove to the vicinity of 

 the i)ubes below. 



The plica semilunaris, or fold of Douglas, on the other hand, is the name 

 given to the lower edge of the posterior sheath of the rectus, when that muscle 

 pierces the aponeuroses so as to lie behind all of them in the lower fourth of its 

 course. The lowest portion of the aponeurosis of insertion of the ol:)lifjuus internus 

 is closely blended with that of the transversalis abdominis, and is called the con- 

 joined tendon. 



Nerve-supply. — From the anterior primary branches of the lower thoracic 

 nerves, and from the first nerve of the lumbar plexus by means of the ilio-inguinal 

 and ilio-hypogastric nerves. The main branches of these nerves run forwards 

 between this muscle and the transversalis abdominis, and give off their filaments 

 to the internal surface of the muscle; some also are distributed to the muscle by 

 the branches which perforate it in order to supply the external oblique. 



Action. — (1) The fil^res of the muscle being curved tend to flatten upon their 

 (Contraction and so to compress the viscera contained within their concavit}-; they 

 will therefore help in defecation, micturition, parturition, and all expiratory efforts. 

 (2) It will also assist expiration by drawing the lower ril)s downwards. (3) AMren 

 Ijoth muscles act together, they flex the thorax upon the pelvis. They will also 

 flex the lumbar and lower thoracic spine. (4) When the muscle of one side acts 

 alone, or in conjunction with the obliquus externus of the other side, it will rotate 

 the thorax to its own side. (5) The posterior fibres of the muscle will draw down 

 the side of the thorax; it will therefore he a lateral flexor of the thorax and of the 

 lumbar and lower dorsal spine. (6) Acting from the thorax, this muscle will flex 

 the pelvis, rotate it to the opposite side, and by means of its posterior fibres it will 

 act as a lateral flexor of the pelvis. 



Relations. — Superficially, the external oljlique and latissimus dorsi; deeply, 

 the transversalis abdominis. Its lower margin lies for a short distance in front of 

 the inguinal canal, containing the spermatic cord in the male, and the round liga- 

 ment in the female. The conjoined tendon lies internally beneath these structures. 

 The aponeurosis of the internal oblique is also in relation with the rectus muscle, 

 of which it forms the sheath in the upper three-fourths of its extent. 



Variations. — Sometimes the muscle is crossed close to its insertion into the ribs by teudiuous 

 intersections, which probably represent ribs. 



Cremaster 



The cremaster (fig. 285) — named from its action as a suspender of the testicle 

 (xpzijLair-yjp a suspender, from ■/.peij.d-^vuij.i to hang) — is really a detached part of the 

 obliquus internus, forming M'itli the fascia Avhich connects its fibres a thin loop- 

 shaped band, which in the male envelopes the lower part and front of the testicle 

 and spermatic cord. In the female it is either entirely al)sent, or a few filtres upon 

 the front of the round ligament take its place. 



Origin. — The iq)per and deep surface of Poupart's ligament about its middle 

 point. 



Insertion. — (1) Tlie s]»ino. and crest of the ]nibic bone; (2) the front of the 

 fascia propria or infundibuliform fascia, which envelopes the testicle ami sper- 

 matic cord. 



Structure. — The fibres, which differ from all other muscles in their scattered 

 and separate character, spring fleshy from the concavity of Poupart's ligament on 

 the deep aspect of the aponeurosis of the obli({uus externus, in continuation of the 

 origin of the obli(|Uus internus. Three main divisions may be noted: — (1) A 

 series of loops which pass from this origin at dift'erent heights in front of the cord 



