THE ABDOMEN. 



955 



THE ABDOMEN. 



[BY FRED J. BBOCKWAY, M. D., 

 I'emonstrator of Anatomy, College of Physicians and Surgeons (Columbia University) Xew York City.] 



In the early stages of the embryo the "body-cavity" (pleuro-peritoneal 

 cavity) is of large size. Anteriorly (*". e. superiorly in the erect posture) there 

 is developed a comparatively enormous space, called the pericardio-thoracic 

 cavity (Fig. 573. .4.. B and C). There also appears a transverse fold marking 



Ptrural Carities 

 Pleurae 

 Perifardial Gorily 



Ftri!o*eum 



ABC 



FIG. 573. Schematic representation of the serous cavities. (Gegenbanr.) 



off this cavity in part from the future abdominal cavity. This fold, associated 

 with many large veins, is next developed into the primary diaphragm, but its 

 dorsal part is incomplete. This is completed later, constituting the diaphragm 

 as we know it in the adult. The diaphragm is thus made up of a ventral younger 

 part and a dorsal older part. When this posterior part fails of development, 

 there is an opportunity for the * congenital diaphragmatic hernia "' to be present. 



The superior or pericardio-thoracic cavity becomes separated into three dis- 

 tinct compartments (Fig. 573. B and C'). the two lateral being continuous for a 

 time with the abdominal cavity. Thus are formed the four large serous spaces 

 of the body, each one lined with serous membrane. Two are thoracic or pleural, 

 lined with pleura, one is cardiac, defined by the pericardial sac, and one is ab- 

 dominal, lined with peritoneum. 



The word abdomen l is applied to the part of the body lying between the 

 thorax and pelvis : it refers to the largest cavity of the adult body, and is often 

 applied incorrectly to the anterior wall of this cavity. It contains nearly all the 

 digestive apparatus and a part of the urinary system. 



Superficially the abdomen is marked from the thorax above by the costal 

 arches, and below from the pelvis by the crests of the ilia, and from the thighs 

 by Poupart's ligaments. These limits, however, do not correspond with those of 

 the abdominal cavity. This extends high into the thorax to the cupola of the 

 diaphragm. The lowest limit is the so-called " diaphragm of the pelvis " made 

 by the Levator ani and Coccygeus muscles on either side. This great cavity 

 shows a smaller artificial subdivision, the pelvic cavity (Fig. 577) The two are 

 not separated, but the limit between them is taken as the brim of the true pelvis. 



1 Abdo'men comes perhaps from abdere, to conceal. Hyrtl says it is an ancient word applied to 

 the belly of a pregnant pig. Cicero transferred it from swine to man in a sense of contempt. Venter 

 and alrnf were used for belly ; abdomen and its adjective abdominalis finally came into general use. 



