69. =Spine of pubes.=--The spine of the pubes is the best guide to the external abdominal ring. It cannot easily be felt by placing the finger directly over it, since it is generally covered by fat. To feel it distinctly, we should push up the skin of the scrotum and get beneath the subcutaneous fat. If there be any difficulty in finding it, abduct the thigh, and the tense tendon of the adductor longus will lead up to it. The position of the spine of the pubes is appealed to as a means of diagnosis in doubt between inguinal and femoral hernia. The spine lies on the outer side of the neck of an inguinal hernia, on the inner side of the neck of a femoral. The spine of the pubes is nearly on the same horizontal line as the upper part of the trochanter major. In this line, about one full inch external to the spine, is the femoral ring. Here is the seat of stricture in a femoral hernia. 70. =Poupart’s ligament, or crural arch.=--The line of Poupart’s ligament (crural arch) is in most persons indicated by a slight crescent-like furrow along the skin. It corresponds with a line drawn not straight, but with a gentle curve downwards from the spine of the ilium to the spine of the pubes. With the help of the preceding landmarks it is easy to find the exact position of the external and internal abdominal rings, and the direction of the inguinal canal. 71. =Abdominal rings.=--The external abdominal ring is situated immediately above the spine of the pubes. It is an oval opening with the long axis directed obliquely downwards and inwards. Though its size varies a little in different persons, yet as a rule it will admit the end of the little finger, so that we can tell by examination whether it be free or otherwise. To ascertain this, the best way is to push up the thin skin of the scrotum before the finger; then, by tracking the spermatic cord, the finger readily glides over the crest of the pubes and feels the sharp margins of the ring. The position of the internal ring is about midway between the spine of the ilium and the symphysis of the pubes, and about two-thirds of an inch above Poupart’s ligament. 72. =Inguinal canal.=--The position of the external and internal abdominal rings being ascertained, it is plain that the direction of the inguinal canal must be obliquely downwards and inwards, and that its length in a well-formed adult male is from one and a half to two inches, according as we include the openings or not. In very young children the canal is much shorter and less oblique, the inner ring being behind the outer. With the growth of the pelvis in its transverse direction, the anterior spines of the ilia become farther apart, and thus draw the internal ring more and more away from (_i.e._ to the outer side of) the external.