942 



PERITONEUM. 



selves, by using great care in manipulation, 

 that it is not the result of violence ; it exists 

 also in the mesenteries of some animals. 



The arteries that ramify in the great omen- 

 turn are branches of the gastro-epiploica d extra 

 and sinistra, and some anastomosing ones from 

 the colica media which pass round the colon 

 and enter the omentum on the side of the in- 

 testine opposite to that on which the artery 

 reaches it. Veins and doubtless nerves accom- 

 pany these arteries, and there are some lym- 

 phatic glands enclosed between the layers of the 

 great omentum along the greater curvature of 

 the stomach. 



The use of the great omentum has never 

 been satisfactorily pointed out. It is peculiar 

 to, and universal in, the class Mammalia, and 

 therefore always co-exists with a diaphragm ; 

 probably it has some reference to the incessant 

 motion and constantly recurring compression to 

 which the intestines are subject from the action 

 of that muscle in respiration. It is frequently 

 seen dipping very deeply between the convo- 

 lutions of the intestines, and occupying their 

 interspaces as a moveable packing material, 

 as if thereby enabling them to retain their 

 cylindrical form whilst subject to incessant 

 disturbance. 



The great omentum, being continuous as one 

 sheet with the splenic omentum, may be re- 

 garded as a great pouch or widening of the 

 mesentery of the stomach. In those animals, 

 such as the Carnivora, which have a very short 

 colon, the great omentum does not extend from 

 the stomach to the colon, but from the stomach 

 to the pancreas, or to a transverse line of attach- 

 ment corresponding in position with that of the 

 transverse part of the duodenum in the human 

 subject. The large intestine in these animals 

 crosses over the small intestine at a point very 

 near the termination of the latter in the crecum, 

 that is to say, over the lower part of the ileum, 

 where it usually has a proper mesentery.* 



The annexed drawing represents the abdo- 

 minal viscera of a lizard. There is a prepa- 

 ration, showing the same parts of a lizard, 

 in the Hunterian collection, (No. 444 D, Phy- 

 siological Series.) The whole of the intestines 

 of this animal, from the oesophagus to the 

 rectum, are connected to the posterior abdo- 

 minal parietes by one continuous mesentery 

 attached along the mesial line. In the sheet 

 situated anterior to the stomach, connecting 

 that organ to the liver and enclosing the gall- 

 duct in its free edge, we recognise the lesser 

 omentum in what we heretofore considered its 

 typical position. In that part of the mesentery 

 which connects the upper part of the stomach 

 to the posterior parietes we recognise the sple- 

 netic omentum ; the spleen is seen enclosed 

 between its layers apparently a large mesen- 

 teric gland. That part of the common mesen- 

 tery which, immediately succeeding the last 

 mentioned, connects the middle and lower part 

 of the stomach to the parietes, we cannot help 

 regarding as the great omentum (the pancreas 



* In some Carnivora, as the cat, the large intes- 

 tine cannot be said fairly to pass over the small in- 

 testine at all. 



Fig. 491 . 



Abdominal viscera of a Lizard. 



a, stomach ; b, liver; c, lesser omentum ; d, gall- 

 duct ; e, duodenum ; f, pancreas; g, great omen- 

 tum ; h, spleen; i, coecum ; k, ovary and kidney; 

 I, lung. 



is just below this). Now pouch out this part 

 towards the left, and a great omentum, such as 

 is found in the Carnivora, is produced, with the 

 same relation of other parts, except in the obli- 

 quity of the parietal attachment in the last- 

 named animals, which is but slight. We have 

 but to enclose the transverse colon between the 

 layers of this sac, to obliterate that portion of 

 the mesentery which is connected to the pan- 

 creas and duodenum, and to carry the trans- 

 verse portion of the latter across just in the line 

 of parietal attachment, in order to produce the 

 condition of the parts which exists in man. It 

 will readily be perceived how, in the mean 

 time, a foramen of Winslow will have been 

 formed by this imaginary manipulation.* We 

 should deem this pouching or widening of the 

 gastric mesentery to have reference to the great 

 distention to which the stomach is liable, but 

 that the sac is far too ample to be obliterated by 

 any possible distention of that organ. 



The transverse mesocolon, formed of two 

 layers of peritoneum, derived as described above, 

 is about six inches broad in the middle, and 

 gradually narrows off on each side. It retains 

 the transverse portion of the colon in situ, and 

 transmits the veins, arteries, and nerves to this 

 part of the intestine. At its root its two layers 

 separate, leaving a prismoid space, which gives 



* The whole duodenum of many mammalian 

 animals, the cat for instance, has a mesentery ; in 

 that case the lower boundary of the foramen of 

 Winslow is determined by the hepatic artery ; in 

 these animnls this portion of the alimentary tube 

 passes off downwards, so that no part of it is trans- 

 verse. 



