1158 THE DIGESTIVE SYSTEM. 



particularly, constitute on each side weak points in the abdominal wall, through which 

 a piece of intestine occasionally makes its way, giving rise to inguinal or femoral 

 hernia respectively. Similar protrusions may also occur at other points in the 

 abdominal wall, and also through apertures in the pelvic wall. 



Tela Subserosa t (O.T. Extraperitoneal or Subperitoneal Connective Tissue). 

 Between the fascia which covers the deep surfaces of the abdominal muscles, and the 

 peritoneum which lines the cavity, there is found a considerable quantity of con- 

 nective tissue, generally more or less loaded with fat, which is known as the. 

 tela subserosa. It is part of an extensive fascial system which lines the whole 

 of the body cavity, outside the various serous sacs, and it is continued on the 

 several vessels, nerves, and other structures which pass from the trunk into the 

 limbs and neck. 



In the abdomen it is divisible into a parietal and a visceral portion, both com- 

 posed of loose connective tissue. The former -lines the cavity, whilst the latter 

 passes forwards between the layers of the mesenteries and other peritoneal folds tc 

 the viscera. The two portions of the extraperitoneal tissue are perfectly continu- 

 ous with one another, and contain in their whole extent a vascular plexus, througl 

 which a communication is established between the vessels of the abdominal wall 

 on the one hand, and those of the contained viscera, on the other. 



The parietal portion is thin and comparatively free from fat over the roof anc 

 anterior wall of the abdomen, and there the peritoneum is more firmly attachec 

 than where the tissue is fatty and large in amount. In the pelvis minor, on th( 

 other hand, the tissue is loose and fatty, and, as such, it is continued up for some 

 inches on' the anterior abdominal wall above the pubes, to permit of the ascent o 

 the bladder during its distension, in the interval between the peritoneum and th< 

 anterior abdominal wall. There also the urachus and the obliterated umbilica 

 arteries will be found passing up in its substance. On the posterior wall thi 

 tissue is large in amount and fatty, particularly where it surrounds the grea ! 

 vessels and the kidneys. 



From the parietal portion the visceral expansions are derived, in the form o 

 prolongations around the various branches of the aorta. Those expansions ar 

 connected with the areolar coats of the blood - vessels and are conducted b; 

 them into the mesenteries and other folds of the peritoneum, and thus reach th 

 viscera. 



The chief uses of the tela subserosa are : (1) to unite the peritoneum to the fascia 

 and muscular layers of the abdominal wall ; (2) to connect the viscera to those wall; 

 and to one another in such a loose manner that their distension or relaxation ma; 

 not be interfered with. That would not be the case if the connecting medium wer j 1 

 firm or rigid ; (3) in addition, it is a storehouse of fat, forms sheaths for the vessel 

 and nerves, and establishes, through its vascular plexus, communication betwee: 

 the parietal vessels and those distributed to the abdominal viscera. 



Subdivision of the Abdomen Proper. Owing to the large size of the cavity 

 and in order to localise more correctly the position of the various organs containe 

 within it, the abdomen proper is artificially subdivided by two horizontal and tw 

 sagittal planes (Fig. 913). 



Of the two horizontal planes, one divides the trunk at the level of the lowe 

 border of the tenth costal cartilage ; this is known as the subcostal plane, an 

 the line where it intersects the abdominal wall is the subcostal line. The secon 

 horizontal plane is at the level of the highest point of each iliac crest which i 

 visible from the front ; this point corresponds to the tubercle seen on the extern* 

 lip of the crest, about t\vo inches posterior to the anterior superior spine, and ca 

 be easily located ; the line and plane are consequently known as the intertubercuk 

 line and plane, respectively. 



The sagittal planes are drawn, one on each side, perpendicularly upwards froi 

 a point on the inguinal ligament midway between the anterior superior spine an 

 the symphysis pubis. The planes and the corresponding lines are known as tt 

 lateral planes and lines respectively. 



By the two horizontal planes the abdomen is divided into three zones, a superi< 

 or costal, a middle or umbilical, and an inferior or hypogastric zone. By the tv 



