ABDOMIXAL PARIETKS AXD MUSCLES 401 



increase greatly the capacity of the sides of the tlioracic cavity. At the same time 

 the abdominal viscera are driven downwards, and as the front part of the parietes 

 is the most yielding, they are also displaced forwards, so as to cause a greater 

 jirominence of this part of the abdomen. In the expulsive efforts of defecation and 

 parturition, after the diaphragm has first contracted in a deep insjnration, and 

 the glottis has been closed so as to prevent the escape of air from the chest, the 

 a])dominal muscles are able to contract with full effect upon the viscera, which 

 have been pressed down by the previous descent of the diaphragm. 



The lower six ribs are slightly elevated by the diaphragm, and the hypc^chondria 

 somewhat dilated, this latter movement being due to the forward and outward 

 pressure of the depressed viscera. 



Relations. — Above lie the pleurse and pericardium, the heart and the lungs. 

 Below are the peritoneum, the liver with its ligaments, the stomach, the spleen, 

 pancreas, kidneys, and suprarenal capsules. The dome-shaped upper convex sur- 

 face rises higher upon the right than the left side. On the right side, being raised 

 by the liver, it reaches to the level of the junction of the fifth costal cartilage with 

 the sternum, and on the left side only to the level of the junction of the sixth 

 costal cartilage. 



Variations. — Tlie oesophageal opening has been found in the right eras, instead of being 

 surrounded by decussating fibres from both crura. The sternal portion of the muscle is not 

 unfrequently absent. 



THE ABDOJIIXAL PARIETES 



The superficial fascia covering the walls of the aljdomen is continuous with that 

 of the thorax and lower limbs, and is usually divided into two layers. 



The first layer is w^ell provided with fat, which in many individuals attains to 

 a considerable thickness, especially in the lower part of the anterior wall. 



The second or deep layer (.Scarpa's fascia) is of a more membranous character 

 and contains a quantity of elastic fibres. Xear the groin it is sej^arated from the 

 more superficial layer by blood-vessels and lymphatic glands. Upon its deeper 

 surface it is loosely connected with the deep fascia which invests the external 

 oblique muscle; but it is closely blended with the linea alba, the fibrous structures 

 in front of the pul)ic bones, the fascia lata innnediately below Poupart's ligament, 

 and the crest of the ilium. 



Both layers are continued downwards upon the external genital organs. In 

 the male they lose their fat and blend w4th the suspensory ligament of the penis, 

 the fascia covering that organ, and the dartos and septum of the scrotum. In the 

 female the}' are continuous with the superficial fascia of the vulva. 



THE ABDOMINAL JIUSCLES 



The muscular portion of the abdominal wall forms a lozenge-shaped figure of 

 which the vertical diagonal extends from the ensiform process to the symphysis 

 pubis, while the transverse encircles the alxlomen from tij) to tip of the transverse 

 processes of the third luml)ar vertebra. 



The V)oundaries of this muscular wall are formed, above by the costal cartilages 

 of the six lower ribs; behind, by the tips of the transverse processes of the lumbar 

 vertebra' ; below, Ijv the crests of the ilia and the pubes. More accurately, each 

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