OF THE ABDOMEN 



431 



divides into two lamellae, which pass, one in front and the other behind the muscle. 

 enclosing it in a kind of sheath, and reuniting on its inner border at the linea alba; 

 the anterior layer is blended with the aponeurosis of the External oblique muscle; 

 the posterior layer with that of the Trfl.nsyprsfl.Hs. Along the lower fourth tlj 

 aponeurosis passes altogether Jn front of the Rectus withoyt any separation.. 

 Where the aponeurosis ceases to split, and passes altogether in front of the Rectus 

 muscle, a deficiency is left in the sheath of the Rectus behind; this is marked above 

 by a sharp lunated margin which has its concavity downward, and is known as 

 the semilunar fold of Douglas (linea semicircular is) (Fig. 325). 



Relations. By its superficial surface the Internal oblique is in relation with the External 

 oblique, Latissimus dorsi, spermatic cord, and external ring; by its deep surface, with the Trans- 

 versalis muscle, the lower intercostal vessels and nerves, the iliohypogastric and the ilioinguinal 

 nerves. Near Poupart's ligament it lies on the fascia transversalis, internal ring, and spermatic- 

 cord. Its low y er border forms the upper boundary of the inguinal canal. 



External oblique - 



Internal oblique 



Linea alba 



Transversalii 



FIG. 323. Diagram of sheath of rectus. 



Fi<;. 324. Diagram of a transverse section through the anterior abdominal wall, below the semilunar 



fold of Douglas. 



The Cremaster muscle (m. cremaster) (Fig. 321) is a thin layer of muscle, com- 

 posed of a number of fasciculi which arise from the inner part of Poupart's liga- 

 ment, where its fibres are continuous with those of the Internal oblique and also 

 occasionally with the Transversalis. It passes along the outer side of the spermatic 

 cord, descends with it through the external abdominal ring upon the front and 

 sides of the cord, and forms a series of loops which differ in thickness and length 

 in different subjects. Those at the upper part of the cord are exceedingly short, 

 but they become in succession longer and longer, the longest reaching down as 

 low as the testicle, where a few are inserted into the tunica vaginalis. These 

 loops are united by areolar tissue, and form a thin covering, the cremasteric fascia, 

 over the cord and testis. The fibres of this muscle ascend along the inner side 

 of the cord, and are Inserted by a small pointed tendon into the crest of the os 

 pubis and in front of the sheath of the Rectus muscle. 



It will be observed that the origin and insertion of the Cremaster is precisely similar to that 

 of the lower fibres of the Internal oblique. This fact affords an easy explanation of the manner 

 in which the testicle and cord are invested by this muscle. At an early period of fetal life the 

 testis is placed at the lower and back part of the abdominal cavity, but during its descent toward 

 the scrotum, which takes place before birth, it passes beneath the arched fibres of the Internal 

 oblique. As the testis and cord go to their destination in the scrotum they pass beneath this 



