The laminw of the mesentery pass back wards and outi,vards along the sides of the spine, and entering the lumbar regions become continuous with the right and left mesocolons, By their divergence in front of the spine they form a triangular enclosure, the basis of which is formed by the bodies of the vertebrm. In this space we find the aorta, and lower down the primitive iliac arteries, the commencement of the thoracic duct, the receptaculum chyli, and several tributary lymphatics and lacteals with their ganglions, the vena cava ascendens, and the left renal vein, the lumbar arteries and veins, and many nervous ramifications from the sympathetic, and more on the sides the lumbar ganglia of the same nerve; here also we notice the fibrous insertions of the crura of the diaphragm, and the anterior common ligament of the vertebra2. Each lamina of the mesentery, as it passes outwards, crosses over the ureter lying on the psoas muscle, and the spermatic artery with the accompanying veins, and some of the musculo-cutaneous branches of the lumbar plexus, and having entered the lumbar region, covers the right and left colons, forming, at its reflections on and off the intestine, the mesocolons. Each of these portions of the colon lies very nearly con nected to the posterior wall of each lumbar region, having only the lower portion of the kidney, with its surrounding adeps, interposed above. In some instances a mesocolon does not exist, and the colon is bound down to the posterior wall of the lumbar region, so that the posterior surface of the intestine uncovered by peritoneum is in direct contact with the quadratus lumborum muscle or the kidney, having only cellular membrane or fat inter vening, and this occurs much more frequently at the left than at the right side : hence the not uncommon occurrence of lumbar abscess, or renal abscess, or calculi being discharged into the colon, and so finding their way out by stool. The proximity too of the portions of the colon to the ureters serves, as Velpeau has remarked, to explain how pins, or beans, or pieces of lead find their way into the bladder and become the nuclei of calculi there, or being impeded in their progress through the ureter, the calculous matter concretes around them in that canal. In confirmation of this explanation, he relates a case which occurred at La Pitie. A pin, the head of which was still found in the colon, in which it had excited considerable ulceration, had passed also into the ureter, so that a calculus, of which the pin formed the axis, projected partly within and existed partly without the canal of the ureter.* Whether the mesocolons exist or not, the right and left colons are in general so fixed in situ, that they rarely form the contents of a hernial sac.
Hypogastric region.—The central portion of this region is occupied by the continued con volutions of the small intestine. The right iliac region is in general entirely or almost entirely occupied by the ccecum, which sometimes has a mesoccecum and sometimes not. In the latter case, a little reticular cellular membrane, and the fascia iliaca, are all that separate the intestine from the surface of the iliacus in ternus muscle. Beneath the fascia the ilio scrotal and the inguino-cutaneous nerves are seen passing outwards to their destination. The internal iliac artery and vein lie along the inner margin of the psoas muscle, covered by a thin fibrous expansion, which is a process from the iliac fascia, and deeply seated between the psoas and iliacus internus muscles is the ante rior crural nerve. The external iliac arteries are crossed at their origin by the ureters, and along their course a few glands may be found either at the sides or in front. This region is
one of great interest to the pathologist, in con sequence of the frequent occurrence of disease in it, whether originating in the wall or in the ccecum.
There is no part of the intestinal canal in which accumulations are more likely to take place than in the ccecum ; and it is now pretty well ascertained by the researches of various observers that inflammation is often pro pagated from the ccecum distended with har dened fa2ces to the cellular tissue and muscles of the iliac fossa, thus exciting abscess, which may open either externally through the abdo minal parietes or internally into the ccecum.* By careful manual examination of the anterior abdominal wall corresponding to this fossa, we are in general able to detect even a slight distension of the ccecum, and percussion em ployed here will often afford considerable assistance in forming a diagnosis. The ver miform appendix of the ccecum frequently hangs down into the pelvic cavity connected to the ccecum by a fold of serous membrane; at other times it lies in the iliac fossa, being folded up under cover of a projecting portion of the ccecum, sometimes as a natural result, and at others as an effect of morbid adhe sions.
The left iliac fossa contains the sigmoid flexure of the colon, which from its cylindrical form, as well as from the circumstance of its being in general much contracted, does not occupy that region to the same extent as the right side is filled by the ccecum. The sig moid flexure is here connected by a mesocolon similar to that of the descending colon, and its relations to the other parts contained in the iliac fossa are pretty much the same as those of the ccecum on the right side. In the centre of the hypogastric region we observe that the posterior wall is formed by the last lumbar vertebra and the promontory of the sacrum, and this region is open below, whereby it com municates with the pelvis through the superior outlet. Hence along the posterior wall we find the rectum with its mesorectum,the middle sacral artery, and the hypogastric plexus of nerves; and some of the pelvic viscera under particular conditions pass forwards into this region, and even admit of being examined during life through the anterior wall. Thus the bladder under distension comes forward, and, as the distension increases, ascends, so as often to occupy the whole of this region to the ex clusion of its natural contents; so also the uterus. The vas deferens in the male and the round ligaments of the uterus in the female, and in both the obliterated umbilical arteries, the urachus and the spermatic vessels, are also among the parts belonging to the hypogastric region.
The preceding account of the abdominal cavity as it is found upon dissection, has re ference chiefly to the adult male subject; but there are certain differences in the relations and positions of parts, dependent on sex and age, to which it is highly important to pay due attention. In the adult female, the chief dif ference arises out of the great size of the pelvis and the consequent increase in the magnitude of the lower part of the abdomen, the trans verse measurement of which will be found to exceed that of the epigastric region, more especially where that region has been arti ficially compressed and consequently dimi nished in its capacity, by the custom of wear ing tight stays. During pregnancy, which, as being a natural change, may be not inap propriately noticed here, the female abdomen experiences a very considerable alteration in its form, capacity, direction, the relations of its organs, and the order of its circulation.