304 Abdominal Muscles 



behind the rectus. Thus the sheath of the rectus is duly formed. 

 The lower part of the rectus is naked on its posterior aspect ; for in 

 the hypogastric region the internal oblique does not split, but, fusing 

 with the aponeurosis of the transversalis, passes over the rectus to the 

 linea alba and pubic crest. This fusion constitutes the conjoined 

 tendon of internal oblique and transversalis, which is attached just 

 behind the external abdominal ring. Except for this tendon backing 

 the ring, inguinal herniae would be much more common. 



In its course from the outer half of Poupart's ligament to the pubic 

 crest the internal oblique does not arch clean over the cord ; some of 

 its lower border is carried down in front of the cord as looped mus- 

 cular fibres and connective tissue ; this is the cremaster or cremasteric 

 fascia (/cpf/xao-roy, hanging), and, like the inter-columnar fascia, 

 beneath which it is placed, it gives a covering to the cord and to an in- 

 guinal hernia ; over old herniae the cremaster is thick and conspicuous. 

 Under the stimulus of cold, the cremaster retracts the testicle ; its 

 nerve is derived from the genito-crural. 



Posteriorly there is no free border to the internal oblique, as the 

 muscle there arises from the lumbar fascia. 



The transversalis is named from the direction of its fibres. It is 

 the deepest of the flat muscles and arises from the inner surface of the 

 lower six ribs (where it inter-digitates with the diaphragm), from the 

 lumbar vertebrae, from the inner lip of the iliac crest, and from the outer 

 third of Poupart's ligament. The lateral part of the muscle is fleshy, but 

 as the fibres approach the linea semilunaris they are condensed into 

 an aponeurosis which passes with the posterior lamella of the internal 

 oblique behind the rectus, except in the lower part, where the trans- 

 versalis ends in the conjoined tendon, as already pointed out. 



The loin-part of the muscle arises in three aponeurotic layers, of 

 which the most superficial is the strongest the fascia lumborum 

 it comes from the tips of the spinous processes. The middle sheet 

 passes between the erector spinae and the quadratus lumborum to the 

 tips of the transverse processes, and the anterior passes over the quad- 

 ratus to the front of the transverse processes, as shown in the figure 

 next above. The lowest border of the transversalis is free, arching 

 high over the cord, and giving no covering to it or to a hernia. 



The separation between the flat muscles of the abdomen is indi- 

 cated by thin planes of connective tissue. In the neighbourhood of 

 the iliac crest the deep epigastric vessels course between the internal 

 oblique and transversalis, as shown on p. 156. 



The rectus arises from the upper part of the pubes by a flat 

 tendon which quickly becomes fleshy, and, widening as it ascends, is 

 inserted into the front of the cartilages of the lowest true ribs. The 

 segmentation of the muscle has been already alluded to (p. 296), 

 and an account of the formation of its sheath is given above. 



The lower part of the muscle is not inclosed in a sheath, its pos- 



