314 MUSCLES AXD FASCIiE OF THE ABDOMEN. 



return from the elevated and bent condition into which they had been thro'mi 

 by the inspiratory forces. In more forcible acts of expiration, in muscular 

 efforts of the limbs and trunk, and in efforts of expulsion from the thoracic and 

 abdominal cavities, all the muscles which tend to depress the ribs, and those 

 which compress the abdominal cavity, concm- in powerful action to empty the 

 lungs, to fix the trimk, and to expel the contents of the abdominal viscera. (See 

 further, " Action of the Abdominal Muscles.") 



MUSCLES AND FASCIA OF THE ABDOMElSr. 



Fascke. — 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 vessels, such as the superficial epigastric and cir- 

 cumflex 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 fi'om the um- 

 bilicus to the pubis, and in the whole length of Ponpart's ligament. 

 At the lower ])art of the linea alba it sends fibrous and elastic processes 

 towards the dorsum of the penis, which form its so-called suspensory 

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

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

 structure : 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 

 united layer acquires a reddish brown colour, and undergoing a 

 modification in structure by being mingled largely with involuntary 

 muscular fibres, constitutes 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 poste- 

 riorly, becomes continuous with the superficial fascia of the perina^um. 



The parts of the sui^erficial fascia here described have received minute attention 

 from surg-ical anatomists, because of their close relation to the seat of hernial 

 tumoiu's ; the adhesion of the fascia to Ponpart's ligament, and its disposition 

 over the inguinal aperture, spermatic cord, and scrotum, while they prevent the 

 descent upon the thigh of matter which has been effused beneath the fascia, 

 cause it rather to spread upwards upon the abdomen or to take its course down- 

 wards upon the scrotum. 



The deep layer of the abdominal fascia is also interesting, as corresponding 

 with fhe tunica ahdoniinali.t, a strong membrane consisting almost entirely of 

 yellow elastic tissue, which exists in animals, as may be well seen in the horse 

 or ox, and which contributes to the support of the viscera. 



Muscles. — The muscular wall of the abdomen is formed for the most 



