336 THE MUSCLES AND FASCIA OF THE TRUNK. 



Nerves. The abdominal muscles are supplied generally by the lower intercostal nerves. 

 The internal oblique and transversalis receive also branches from the ilio-hypogastric and ilio- 

 inguinal nerves, and the cremaster is supplied by the genital branch of the genito-crural 

 nerve. The quadratus lumborum receives small branches from the last dorsal and the upper 

 lumbar nerves. 



Actions. The abdominal muscles not only form a great part of the wall to enclose and 

 support the abdominal viscera, but by their contraction are capable of acting successively on 

 those viscera, on the thorax, and on the vertebral column. When the pelvis and thorax are 

 fixed, the abdominal muscles constrict the cavity and compress the viscera, particularly if the 

 diaphragm be fixed at the same time by the closure of the glottis, as occurs in vomiting and 

 in the expulsion of the foetus, the fasces, or the urine. 



If the vertebral column be fixed, these muscles raise the diaphragm by pressing on the 

 abdominal viscera, draw down the ribs, and contract the base of the thorax, and so contribute 

 to expiration ; but if the vertebral column be not fixed, the thorax will be bent directly for- 

 wards when the muscles of both sides act, or inclined laterally when they act on one side only, 

 or rotated when the external oblique of one side and the opposite internal oblique act in com- 

 bination. 



The quadratus lumborum is a lateral flexor, and to a slight extent also an extensor of the 

 spine when the muscles of the two sides act together. By drawing down the last rib it also 

 aids in inspiration (p. 326). 



If the thorax be fixed, the abdominal muscles may be made to act on the pelvis ; thus, in 

 the action of climbing, the trunk and arms being elevated and fixed, the pelvis is drawn 

 upwards, either directly or to one side, as a preparatory step to the elevation of the lower 

 limbs. 



LINING FASCIA OF THE ABDOMEN. On the inner surface of the wall of the 

 abdomen is a membranous structure which lines the visceral aspect of the deepest 

 stratum of muscles : it is divisible into two principal parts, the transversalis fascia 

 and the iliac fascia. 



The transversalis fascia is named from its position on the deep surface of the 

 transversalis muscle. It is strongest in the lower part of the abdomen, where the 

 muscular and tendinous support is somewhat weaker. Followed upwards from this 

 situation, it becomes gradually slighter, and beyond the margin of the ribs it is 

 continued into a thin areolar layer on the under surface of the diaphragm. Along 

 the inner margin of the iliac crest, between the iliacus and transversalis muscles, the 

 fascia is attached to the periosteum. For about two inches inwards from the 

 anterior superior iliac spine, it is closely connected with the back of Poupart's 

 ligament, arid is there directly continuous with the iliac fascia. Internal to the 

 middle of Poupart's ligament, the external iliac artery and vein, as they pass out 

 into the thigh, intervene between the transversalis fascia and the iliac fascia, and 

 from this point to the edge of Gimbemat's ligament the transversalis fascia is 

 prolonged downwards under Poupart's ligament, and over the vessels, forming the 

 anterior portion of the funnel-shaped femoral sheath. As this prolongation of the 

 fascia passes under Poupart's ligament it is strengthened by a dense band of fibres, 

 constituting the deep crural arch, which curves over the vessels, and is inserted into 

 the pubic spine and the ilio-pectineal line behind the conjoined tendon of the trans- 

 versalis and internal oblique muscles. It includes beneath it, internal to the 

 vessels, a space between Gimbernat's ligament and the vein, sufficiently large to 

 admit the point of the little finger ; this is called the femoral ring, and is the space 

 through which a femoral hernia descends. About midway between the anterior 

 superior iliac spine and the symphysis pubis, and about half an inch above Poupart's 

 ligament, the spermatic cord in the male, or the round ligament in the female, 

 pierces the transversalis fascia. The opening thus made is called the internal or 

 deep abdominal ring (internal inguinal aperture) ; the fascia above and internal to it 

 is thin, but below and external to it is firm and thick, and the lower boundary of 

 the opening is formed by a distinct crescentic edge, over which the cord or round 

 ligament passes : from the margin of the opening a delicate funnel-shaped covering, 



