OF THE A B DOMEX. 



447 



account of the liver ; and the central leaflet the least, because of its connection to 

 the pericardium. In descending the diaphragm presses on the abdominal viscera, 

 and so to a certain extent causes a projection of the abdominal wall ; but in conse- 

 quence of these viscera not yjelding completely, the central tendon becomes a fixed 

 point, and enables the circumferential muscular fibres to act /row it, and so elevate 

 the lower ribs and expand the lower part of the thoracic cavity ; and Duchenne 

 has shown that the Diaphragm has the power of elevating the ribs, to which it 

 is attached, by its contraction, if the abdominal viscera are in situ, but that if these 

 organs are removed, this power is lost. When at the end of inspiration the Dia- 

 phragm relaxes, the thoracic walls return to their natural position in consequence 

 of their elastic reaction and of the elasticity and weight of the displaced viscera. 1 



In all expulsive acts the Diaphragm is called into action, to give additional 

 power to each expulsive effort. Thus, before sneezing, coughing, laughing, and 

 crying, before vomiting, previous to the expulsion of the urine and faeces, or of 

 the foetus from the womb, a deep inspiration takes place. 



The height of the Diaphragm is constantly varying during respiration, the 

 muscle being carried upward or downward from the average level ; its height also 

 varies according to the degree of distension of the stomach and intestines, and the 

 size of the liver. After a forced expiration, the right arch is on a level, in front, 

 with the fourth costal cartilage : at the side, with the fifth, sixth, and seventh 

 ribs ; and behind, with the eighth rib, the left arch being usually from one to two 

 ribs' breadth below the level of the right one. In a forced inspiration, it descends 

 from one to two inches ; its slope would then be represented by a line drawn from 

 the ensiform cartilage toward the tenth rib. 



THE ABDOMEN. 

 Superficial Muscles. 



J Transversalis. 

 . Rectus. 



The Muscles in this region are, the 

 ' Obliquus Externus. 

 N Obliquus Internus. 



Pyramidalis. 



Dissection i'Fig. 291). To dissect the abdominal 

 muscles, make a vertical incision from the ensiform car- 

 tilage to the pubes; a second incision from the umbilicus 

 obliquely upward and outward to the outer surface of the 

 chest, as high as the lower border of the fifth or sixth rib : 

 and a third, commencing midway between the umbilicus 

 and pubes. transversely outward to the anterior superior 

 iliac spine, and along the crest of the ilium as far as its 

 posterior third. Then reflect the three flaps included be- 

 tween these incisions from within outward, in the lines of 

 direction of the muscular fibres. If necessary, the abdom- 

 inal muscles may be made tense by inflating the peritoneal 

 cavity through the umbilicus. 



The Superficial fascia of the abdomen consists 

 over the greater part of the abdominal wall of a 

 single layer of fascia, which contains a variable 

 amount of fat ; but as this layer approaches the 

 groin it is easily divisible into two layers, be- 

 tween which are found the superficial vessels and 

 nerves and the superficial inguinal lymphatic 

 glands. The superficial layer is thick, areolar in 

 texture, containing adipose tissue in its meshes, 

 the quantity of which varies in different subjects. 

 Below it passes over Poupart's ligament, and is 

 continuous with the outer layer of the superficial 

 fascia of the thigh. In the male this fascia is continued over the penis and outer 



1 For a detailed description of the general relations of the Diaphragm, and its action, refer to 

 Dr. Sibson's Medical Anatomy. 



S. Dis- 

 section of 



inguinal 

 hernia. 



FIG. 291. Dissection of abdomen. 



