The position of the epigastric artery with re spect to the neck of the sac at once points out whether a hernia is by the direct descent or not, for it marks the internal or pubic boundary of the internal ring. This vessel is occasionally irregular in its origin, but in its normal or usual state it comes of from the external iliac before it has reached Poupart's ligament, and conse quently in that position it lies behind the brig of the peritoneum, which it passes by forming an arch, the concavity of which is directed up wards. It then appears in front, between the fascia transversalis and the peritoneum, but more closely attached to the former, with which it remains when the membrane is torn away. The vas deferens is seen coming from the pel vis obliquely upwards and outwards until it reaches the spermatic artery, which, having de scended from above, nearly in a perpendicular direction, meets the vas deferens at rather an acute angle, the former being to the outside and nearly in front of the latter. These vessels having passed the fascia transversalis disappear by arching round the epigastric artery and en tering the inguinal canal, and they define the inferior margin of the internal ring. The re mainder of its border is not so very distinctly marked, partly in consequence of a very deli cate fascia which is given off from it and passes down a short way on the spermatic cord, where it becomes indistinct and is lost; and partly because the transversalis muscle lying before it renders the view obscure. The internal border of the internal ring is always (as stated by Sir A. Cooper) midway between the anterior superior spinous process of the ilium and the symphysis pubis.
W hen a protruded viscus, then, is passing through this ring, it has the epigastric artery to its internal or pubic side, and generally the vessels of the cord behind it; but a variety sometimes occurs, for the hernia may protrude exactly at the spot where the spermatic artery and vas deferens meet each other at an angle, and separate these vessels from each other, leaving the artery rather to the outside and in front, the vas deferens still occupying its usual situation behind. After the hernia has passed the fascia transversalis, it is still behind the fibres of the internal oblique and transversalis muscles, and has to pass a few lines (the dis tance varying in different subjects) before it reaches the posterior surface of the tendon of the external oblique. On prosecuting this dis section further by detaching the fascia trans versalis from the transversalis muscle in a di rection downwards and outwards, the intestine will be found to have entered a canal of an inch and a quarter to an inch and a half in length, its direction being obliquely downwards and inwards to the external ring. This is termed the inguinal canal, and is thus formed. Pou part's ligament, whether it be considered as a portion of the tendon of the external oblique or not, is powerfully strong and thick : to it the fascia transversalis is firmly adherent behind, and the thinner and more expanded fibres of the tendon of the external oblique before.
Between these, then, a sheath is formed in which the hernia is lodged, having in front the tendon of the external oblique, and also covered by the cremaster muscle, particularly that part of it which has its origin from Poupart's liga ment. Behind it is the fascia transversalis, and more internally or nearer the pubis the conjoined tendon of the internal oblique and transversalis, and below is Poupart's ligament. Above, it is crossed obliquely by the inferior margin of the internal oblique and transversalis. These muscles have a fleshy origin from the ex ternal third of Poupart's ligament, from which they pass in an arched form to be inserted by a common tendon into the crest of the pubis. Under this arch the viscus slips and thus places itself anterior to the conjuined tendon before passing through the external ring and becoming a scrotal hernia.
.Anatomists have not agreed in their descrip tions of the internal oblique muscle, although a correct and accurate knowledge of the situa tion of it and of the transversalis in the neigh bourhood of the rings is indispensable to the right understanding of hernia. According to Sir A. Cooper* and Lawrence,t the upper part only of the internal ring is shut up by these muscles,leaving the lower unprotected, and con sequently, according to this view of the subject, a hernia on entering the inguinal canal should have them above it. Cloquett states that the inferior border of the transversalis passes on a level with the superior, opening internally, but the edge of the internal oblique is lower down, covers the spermatic cord in the inguinal canal, and passes over it to be inserted intu the pubis at the point a here it escapes from the iVerior opening of the canal, that is, the external ring. Scarpa" gives a different description still, where he says, " towards the side at about eight lines distance from the apex of the ring, the lower muscular fibres of the internal oblique muscle separate from each other to allow the sper matic cord to pass between them ;" and Guthriet considers the occasional passage of a hernia throng], the fibres of this muscle, and its compression by them, to be no unfrequent cause of strangulation. It is not easy to reconcile these conflicting authorities, which in them selves demonstrate the fact that the inferior border of this muscle exhibits some varieties in its relation to the inguinal canal and internal ring according to the extent of its origin from Poupart's ligament. When a hernia is present, I have always seen it arched over the neck of the sac, and although I would by no means assert that a rupture never takes its course between these muscular fibres, yet I have not met with an instance, and as I have observed elsewhere, I imagine such an occurrence would create a deviation from the usual relative anatomy of the cremaster muscle with respect to the hernial sac.—See ABDOMEN.