1220 THE DIGESTIVE SYSTEM. 



which lies between the right and left flexures. It begins at the end of the right 

 flexure, at the point where the colon passes forwards from the anterior surface 

 of the kidney, and, turning to the left, crosses the descending duodenum (Fig. 957). 

 It runs at first transversely to the left, and for the first few inches is compara- 

 tively fixed, being united to the front of the descending part of the duodenum 'and 

 the head of the pancreas either by a very short mesentery or by areolar tissue. 

 Immediately to the left of the head of the pancreas a long mesentery is developed, 

 which allows the colon to hang down in front of the small intestine, at a con- 

 siderable distance from the posterior abdominal wall. The portion of the colon 

 so suspended is therefore very movable, and consequently its position is very variable, 

 and is influenced by posture and by the condition of the other viscera. Towards 

 its left extremity the mesentery shortens again, thus bringing the gut towards the 

 tail of the pancreas (Fig. 957), along which it runs upwards into the left hypo- 

 chondrium, under cover of the stomach, as far as the inferior end of the spleen, 

 where it passes into the left (O.T. splenic) flexure (Fig. 942). Its two ends lie in 

 the right and left hypochondriac regions respectively, whilst its middle portion 

 hangs down into the umbilical, or even the hypogastric region. 



Its average length is about 19 or 20 inches (47'5 to 50*0 cm.), that is, more 

 than twice the distance, in a direct line, between its two extremities. This great 

 length is accounted for by the curved and somewhat irregular course which the 

 bowel pursues. 



Relations. The greater part 'of the transverse colon lies behind the greater 

 omentum, which must consequently be turned upwards in order to expose it. 

 Above, it is in contact, from right to left (Fig. 957), with the liver and gall-bladder 

 (which also descend in front of the colon), the stomach, and, near its left end, with 

 the tail of the pancreas and inferior end of the spleen (Fig. 947). Anteriorly are placed 

 the omentum and the anterior abdominal wall ; towards its termination the stomach 

 also is anterior. Posteriorly, it first lies in contact with the descending duodenum 

 and head of the pancreas; further to the left, where it hangs down, the small intestine 

 is placed below and posteriorly, and it is connected to the posterior abdominal wall 

 (more correctly, to the anterior border of the pancreas) by the transverse mesocolon. 

 It is also loosely connected to the stomach by the gastro-colic ligament which is 

 attached to its anterior surface. The transverse mesocolon and the gastro-colic 

 ligament are described with the peritoneum, p. 1242. 



The transverse colon is completely covered with peritoneum, with the exception 

 of the first few inches of its posterior surface, which are often, if not usually, 

 uncovered. 



The state of the peritoneal covering on the posterior surface of the first part of the transverse 

 colon would seem to depend, in some degree, on the extent to which the liver passes downwards 

 on the right side. With a small, high liver no mesentery is present, and the posterior surface ia 

 devoid of peritoneum ; on the other hand, when the liver is enlarged in the vertical direction, 

 it pushes the colon downwards before it, and brings the upper line of the peritoneal reflection 

 from its back, into contact with the lower, thus giving rise to the mesentery. In the foetus of 

 three or four months every part of the colon is supplied with a long mesentery ; subsequently 

 this, as a rule, disappears at the beginning of the transverse colon, but it may be reproduced in 

 the manner stated. 



Flexura Coli Sinistra (Left Flexure of the Colon (O.T. Splenic Flexure)). 



The terminal portion of the transverse colon runs upwards (also posteriorly and 

 to the left) until the inferior end or base of the spleen is reached ; here it bends 

 sharply, forming the left flexure, and runs down into the descending colon. The 

 flexure is placed deeply in the left hypochondrium, posterior to the stomach, and 

 in contact with the base of the spleen. It lies at a higher level than the right 

 colic flexure, and is' connected to the abdominal parietes by the phrenico-colic 

 ligament, which helps to maintain it in this position. 



Ligamentum Phrenicocolicum (Fig. 947). This is a triangular fold of peritoneum, 

 with a free anterior border, which is attached medially to the left flexure and 

 laterally to the diaphragm opposite the ninth to the eleventh rib. (Owing to the 

 fact that the base of the spleen rests upon it, the ligament has also received the 

 older name of sustentaculum lienis.) 



