262 



ABDOMEN 



shaped diaphragm, which presents a deep concavity towards 

 the abdomen. Inferior -fy, its floor is formed by the pelvic 

 diaphragm, consisting of the levatores ani and the coccygei 

 muscles. The floor also is concave towards the abdominal 

 cavity. Neither the roof nor the floor is complete and 

 unbroken. The diaphragm is perforated by certain struc- 

 tures which pass between the thorax and the abdomen. The 

 continuity of the pelvic diaphragm is broken by the passage 



of certain structures be- 

 tween the pelvic division 

 of the abdominal cavity 

 and the perineum. The 

 upper part of the ab- 

 dominal cavity extends 

 upwards for a consider- 

 able distance under the 

 shelter of the lower ribs 

 and their costal carti- 

 lages. The protection 

 which is thus afforded 

 to the viscera in that 

 portion of the cavity 

 is most complete later- 

 ally and posteriorly. 

 DO / 



'PELVIC 



-SUBCOSTAL 

 PLANE 



NTERTUBERCULAR 

 PLANE 



LINE 



OF 

 PELVIC BRIM 



Anteriorly, a wide A- 

 shaped gap is left be- 

 tween the costal car- 

 tilages of the opposite 

 sides as they ascend 



towards the sternum. 

 FIG. 117. Outline of the Abdominal Cavity , , , . , , 



as seen in median section. The planes of L ne level tO whlch the 

 subdivision are indicated by dotted lines. COStal arches descend 



on each side varies 



greatly in different subjects, but, in the great majority of 

 cases, a .narrow belt of abdominal wall, from one to two 

 inches wide, is left between the lower border of the chest 

 wall and the highest point of the iliac crest. The only 

 skeletal support of that part of the wall lies behind and is 

 provided by the lumbar part of the vertebral column. 



At a lower level, the expanded iliac bones give support 

 to the abdominal walls posteriorly and laterally, whilst, in the 

 lowest part of the abdomen, the pubic, ischial, sacral, and 



