5. Between the internal fibrous expan sion of the abdomen and the peritoneum is a cellular tissue, which presents different cha racters in each region ; it is the subperitoneal cellular tissue. Along the anterior wall it is thin and fine, except inferiorly opposite the in ternal abdominal ring, where it becomes more abundant, as well as in the hypogastric region, immediately above the pubis. In the iliac fossa and lumbar region it is lax and abundant, especially in the latter, where there is also a considerable quantity of fat surrounding the kidney. In the iliac fossa this cellular tissue is stretched across the crural ring, and forms what Cloquet describes under the name of septum crurale. On the superior wall it is ex tremely fine, and in very small quantity. Im mediately behind the sternum, and in the mid dle line, this cellular tissue communicates with that of the mediastinum through a separation of the anterior fibres of the diaphragm.
This subserous cellular tissue forms the pri mary covering of all herniae, which push a peritoneal sac before them, and as being the fascia constituting the nearest investment of the sac, it is generally called the fascia propria.
Opposite the crural canal this cellular tissue is often so abundant, as, when condensed by the pressure of the hernial tumour, to form an ex pansion over the sac of considerable thickness. Sometimes it contains fat, and not unfrequently we find a large lymphatic ganglion in it, filling up the crural ring.
6. Peritoneum.—A considerable part of the abdominal surface of the walls of the abdomen is lined by a very fine transparent serous mem brane—the peritoneum, which is likewise con nected, to a greater or less extent, with every viscus within the cavity. In consequence of this double connexion, it happens that in various situations the peritoneum is reflected from the wall of the abdomen upon an adjacent viscus, and thus are produced various folds of this mem brane, which demand the attention of the ana tomist. These folds are rendered distinct when such a section of the anterior abdominal wall is made as without dividing them to allow of it being held apart from the viscera. I shall enumerate these folds in describing the relation of the peritoneum to the several walls. The anterior wall of the abdomen is entirely lined by peritoneum, and has in connexion with it four folds, all of which, as it were, racjiate from the umbilicus. In the adult these folds are reflected round four ligamentous cords (three of which are the remains of bloodvessels in the foetus), which meet at the umbilicus and diverge, one upwards, backwards, and to the right side (the obliterated umbilical vein), two downwards and outwards towards Pou part's ligament on each side, so as to pass behind the inguinal canal, nearly midway between the two rings ( the obliterated um bilical arteries), and the fourth nearly ver tically downwards along the middle line to be inserted into the apex of the bladder (the ura.
chus). The four folds are similar in direction to that of the fibrous cords contained within them : the fold which passes upwards towards the liver is falciform, the concavity being di rected downwards and backwards. From its connexion with the convex surface of the liver it is also called the falciform ligament of the liver, and the fibrous cord contained in its in ferior margin, the ligamentum teres. The in ferior and external folds pass each from the umbilicus, downwards and outwards to the iliac fossa, to a point a little on the inner side of the internal abdominal ring, where it dis appears, being continued externally over the iliac fossa, and internally behind the rectos muscle. This fold, when stretched towards the umbilicus, evidently forms the partition between two pouches, the external and in ternal inguinal pouches, which correspond re spectively to the internal and external abdo minal rings, and indicate the situations at which make their escape those two forms of inguinal hernia, which, from their connexion with these pouches, are called by Hesselbach external and internal inguinal hernim; the for mer being that by oblique descent, the latter that by direct descent.
The fourth or vertical fold indicates the reflection of the peritoneum from the anterior abdominal wall upon the superior fundus and posterior surface of the bladder : when that viscus is empty and contracted, this fold dis appears totally ; it is more apparent when the bladder is partially filled, and is still more distinct in the foetus in consequence of the greater size of the urachus at that period. Just above the pubis the peritoneum is con nected to the abdominal wall by a very lax cellular tissue; and accordingly when the blad der is much distended, the peritoneum is pushed upwards, and stripped off the abdo minal wall to an extent proportioned to the degree of distension of the bladder, so that its anterior surface is then in immediate contact with the abdominal wall, and may be opened with impunity so far as the peritoneum is con cerned.