FASCLE OF THE ABDOMEX. 257 



If the vertebral column be fixed, these muscles press up the diaphragm, draw- 

 down the ribs, and contract the lower border of the thorax, and so contribute 

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

 directly forwards, when the muscles of both sides act, or rotated to either side, 

 should they act alternately. Thus, if the external oblique of the right side be 

 made to act on the thorax, the first effect appears to be that of drawing its 

 margin down towards the pelvis; but, if the effort be continued, the trunk 

 will be rotated towards the opposite side. The left internal oblique may co- 

 operate in this action, for the direction of its fibres coincides with that of the right 

 external oblique. 



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. 



The attachment of the tendinous intersections of the rectus muscle to the anterior 

 wall of its sheath, causes the formation of corresponding transverse folds during its 

 contraction, and may enable the separate parts of the muscle to act on different 

 portions of the abdominal wall. By the same arrangement, when the oblique and 

 transverse muscles contract, the breadth of the recti will be maintained and even 

 increased ; and these muscles will thus be enabled, both in the straight and in the 

 incurved position of the abdominal wall, more effectually to compress the abdominal 

 viscera. The pyramidalis muscle assists the inferior part of the rectus. 



FASCLE OF THE ABDOMEN. 



The superficial fascia of the abdomen is usually described as consisting of 

 two layers. One of these, the subcutaneous layer, corresponds in its general 

 features with the areolar subcutaneous tissue of other parts of the body, 

 and contains embedded in it a very variable and often large quantity of fat. 

 The other, or deeper layer, is of a denser and more membranous structure, 

 contains a considerable amount of yellow elastic tissue in its substance, and 

 is united by intervening fibres, in some places very closely, to the aponeurosis 

 of the external oblique muscle. These two layers are both continuous with 

 the superficial fascia on other parts of the trunk : they can be dissected as 

 distinct layers only on the fore part of the abdomen, and are separated in a 

 more marked manner in the lower part of its wall, where subcutaneous ves- 

 sels, such as the superficial epigastric and circumflex iliac, lie between them. 

 The deep or elastic layer of the superficial fascia is bound down by a thin 

 but dense intervening layer of fibrous tissue to the aponeurosis of the 

 external oblique muscle in two places more particularly, viz., along the linea 

 alba from the umbilicus to the pubes, and in the whole length of Poupart's 

 ligament. At the lower part of the linea alba it sends fibrous and elastic 

 processes towards the dor.su rn of the penis, which form its so-called sus- 

 pensory ligaments. By its close union to Poupart's ligament, it comes into 

 relation with the fascia lata of the thigh, which is also united to that struc- 

 ture : but in the neighbourhood of the external inguinal aperture it remains 

 free, and is prolonged downwards over the spermatic cord to the scrotum. 

 The subcutaneous layer, losing its fat, is combined with the deeper layer as 

 they both pass to the scrotum ; and here the layer which they form acquires 

 a reddish brown colour, and undergoes a modification in structure by being 

 mingled largely with involuntary muscular fibres, and thus forms the dartos 

 tunic of the scrotum. Some involuntary muscular fibres also exist in the 

 altered superficial fascia which covers the penis. This covering, on leaving 

 the scrotum posteriorly, becomes continuous with the superficial fascia of 

 the perinseuni. 



