The anastomosis which exists between the obturator artery (when that vessel is derived from the internal iliac) and the epigastric, by means of those small branches of each which ramify behind the pubes, serves to afford some explanation of one of the most striking instances of variety of origin met with in the arterial system, viz., the transfer of the origin of the obturator from the internal iliac to the epigastric artery.
Or at least, it may be said that the various modes in which the connection between the two arteries is established in different cases, demonstrate the easy steps by which the obturator may be said to pass from one place of origin to the other. The anastomosis referred to is itself, in fact, the first stage in a series of varieties which have been observed connecting the ordinary mode of origin of the obturator (from the internal iliac), with that in which it arises from the epigastric. In the next stage, illustrated in another case, one of the anastomotic branches is a little enlarged in size, andforms a tolerably direct communication between the two vessels ; then the anastomotic branch from the epigastric enlarges still more, whilst the posterior or usual obturator branch is proportionably diminished, in which case the obturator artery may be said to have two equal roots ; a further diminution of the posterior branch, and a corresponding increase of that from the epigastric, coNducts us to the final step, viz., the reduction of the former to the size of a small anastomosing branch, and the concurrent enlargement of the latter, which now becomes the only root or origin of the obturator artery. In this last-mentioned case, therefore, the obturator may be said to arise from the epigastric artery, and to receive a small anastomosing branch from the internal iliac, an arrangement the converse of that described at the commencement of these observations.
The relative frequency with which these various conditions of the obturator artery are met with, in a large number (361) of cases examined, may be thus shortly stated : —
In 2 cases out of 3, the obturator artery arose from the internal iliac.
In one case in 3, from the epigastric.
In a very small number of cases (about 1 in 72), (by two roots) from both the above-named vessels. And in about the same proportion, from the external iliac artery.
Cloquet presents the following table as the result of an examination of 250 cases :
|Normal origin of the obturator artery from the internal iliac||160|
|From the epigastric artery on both sides||56|
|Do.||do.||on one side only 28|
Sometimes the obturator artery arises from the epigastric on both sides of the same body, but, in the majority of instances, this mode of origin of the vessel is met with on one side only.**
When the obturator artery arises from the epigastric it turns backwards into the pelvis to reach the canal at the upper part of the thyroid foramen ; and in this course it is necessarily close to the femoral ring — an opening at the inner side of the external iliac vein, through which hernial protrusions descend from the abdomen into the thigh. The artery is usually directed backwards close to the iliac vein, and therefore lies to the outer side of the femoral ring ; but it occasionally crosses behind the ring, and, in some cases, curves to its inner side. The position of the vessel in such cases, and the practical inferences to be deduced from it, will be again referred to in the anatomical history of the parts concerned in femoral hernia.
* Traite d'Anatomie Descriptive. Paris 1836.
** This does not agree with the table just presented as the experience of Cloquet.]