Surgical Anatomy.-To the surgeon the anatomy of the abdominal wall presents a very special interest from the bearing which it has upon Hernia or Rupture.

Hernia abdominis may be defined as being the protrusion of any viscus or portion of a viscus, or the protrusion of any portion of a peritoneal fold (e.g., great omentum) through the wall of the abdomen. There are three localities in which, from natural weakness of the parietes, this protrusion is specially liable to occur (1) through the external abdominal ring, which gives passage to the spermatic cord in the male, and the round ligament of the uterus in the female; (2) through the crural canal or innermost compartment of the femoral sheath, within which certain lymphatic vessels ascend from the thigh into the abdominal cavity; (3) through the umbilicus or the foramen in the linea alba of the foetus, which transmits the constituents of the umbilical cord. These different forms of hernia are distinguished by the terms-inguinal, femoral, and umbilical.

There are other situations at which hernial protrusions occur, but so rarely that it would be out of place to take notice of them here.

Inguinal Hernia. -The inguinal canal is not so great a source of weakness to the abdominal wall as might, at first sight, be expected, and this chiefly on account of its obliquity of direction. The inlet or internal abdominal ring is situated a long way (fully an inch and a half) to the outer side of the outlet or external abdominal ring. The canal is therefore distinctly valvular; the greater the force with which the viscera are pressed directly against the inguinal part of the abdominal parietes, the more firmly will the posterior wall of the canal be pressed against the spermatic cord and the anterior wall.

On the left side of the body the parts related to inguinal hernia have been retained in position. The student should, therefore, make a dissection of the inguinal region, with special reference to hernia. Begin by reflecting the aponeurosis of the external oblique. Make a vertical incision through it parallel to the outer border of the rectus, and carry it downwards on the inner side of the internal pillar of the external abdominal ring. The aponeurosis can thus be thrown downwards and outwards, and the external ring, at the same time, preserved. The internal oblique, cremaster, and conjoined tendon should now be cleaned, and their precise relations to the spermatic cord studied. Notice that the fleshy lower border of the internal oblique overlaps the upper part of the cord, whilst, towards the outlet of the inguinal canal, the conjoined tendon lies behind the cord. Next replace the aponeurosis of the external oblique, and, introducing the point of the forefinger into the external abdominal ring, press directly backwards. Observe that it rests upon the conjoined tendon; that, in fact, this tendon and the fascia transversalis alone intervene between the finger and the extra-peritoneal fatty tissue and the peritoneum. The lower part of the internal oblique muscle should now be separated from the transversalis by insinuating the handle of the knife between

them. When this is done, divide the internal oblique close to Poupart's ligament, and throw it forwards. At the same time, make a longitudinal incision through the cremaster muscle, and turn it aside from the surface of the cord.

All further dissection must be effected from the inside. Divide the abdominal wall horizontally, from side to side, at the level of the umbilicus. Raising the lower part of the abdominal wall, and examining its posterior surface, the student will observe three peritoneal ridges or falciform folds radiating from the umbilicus as from a centre, and proceeding downwards towards the brim of the pelvis. These are caused by the presence of three fibrous cords, the urachus and the two obliterated hypogastric arteries,-in the extra-peritoneal fatty tissue. The urachus occupies the middle line, and extends downwards to the apex of the bladder. The obliterated hypogastric artery proceeds downwards and outwards on each side so as to gain the side of the bladder. It lies a short distance to the inner side of the internal abdominal ring.

There is still another peritoneal ridge or fold on this aspect of the abdominal wall. It is formed by the deep epigastric artery as it passes upwards and inwards to reach the deep surface of the rectus abdominis muscle. It is placed a short distance to the outer side of the fold which corresponds to the obliterated hypogastric artery, and runs more or less parallel to it.

By these three peritoneal folds three fossæ, which vary greatly in depth in different subjects, are formed on either side of the middle line, close to Poupart's ligament. They are termed the external, middle, and internal inguinal pouches, and are very generally regarded as determining, to a certain extent, hernial protrusions in this region. The internal inguinal fossa lies between the folds formed by the urachus and the obliterated hypogastric arteries, and the external abdominal ring or the outlet of the inguinal canal corresponds to its outer and deepest part. The middle inguinal fossa, very narrow but frequently very deep, is situated between the peritoneal folds which enclose the obliterated hypogastric artery and the deep epigastric arteries. The bottom of this fossa corresponds to the outer part of the posterior wall of the inguinal canal, or, in other words, to that part of the posterior wall which is formed by the fascia transversalis. The external inguinal fossa is placed to the outer side of the deep epigastric artery, and its lower, inner, and deepest part corresponds to the internal abdominal ring.

The student has already seen, in the dissection of the abdominal wall, that the deep epigastric artery, together with Poupart's ligament and the outer border of the rectus, bound a triangular space termed Hesselbach's triangle. Recalling this fact, he will understand that the obliterated hypogastric artery, which lies to the inner side of the deep epigastric, must ascend in relation to the posterior aspect of the floor of the triangle and cut the space into two.

Having determined these points, the dissector can proceed as follows:-Divide the lower part of the abdominal wall in a vertical direction along the linea alba, from the umbilicus to the pubes. Make this incision a little on one side of the urachus, and, on nearing the pubis, be careful not to injure the bladder, which may project upwards beyond it. On throwing the left flap downwards and outwards, it may be possible to detect the position of the internal abdominal ring from the fact that in some cases the peritoneum is slightly dimpled into it. This dimple or depression is termed the digital fossa. Now strip the peritoneum from the flap as far down as Poupart's ligament. This can be easily done with the fingers, as its connection with the extra-peritoneal fatty tissue is very slight. Next separate the extra-peritoneal fatty tissue from the fascia transversalis with the handle of the knife, proceeding with great care as Poupart's ligament is approached. The internal abdominal ring, or the inlet of the inguinal canal, is now seen from within. From this point of view the opening is more like a vertical slit in the fascia transversalis than a ring. Its lower and external margin will be seen to be specially strong and thick. Note the deep epigastric artery passing upwards and inwards close to its inner margin. Further, observe the vas deferens and the spermatic vessels entering it, the former, as it disappears into the canal, hooking round the deep epigastric artery. Introduce the tip of the little finger into the opening and push it gently downwards in the direction of the inguinal canal. On raising the flap of the abdominal wall and looking at its front aspect, a very striking demonstration of the infundibuliform fascia can thus be obtained.

There are two forms of Inguinal Hernia,—viz, oblique and direct. Oblique inguinal hernia follows the course of the spermatic cord. The protrusion traverses the entire length of the inguinal canal, entering at the inlet or internal abdominal ring, and emerging (when the hernia is complete) at the outlet or external abdominal ring. Direct inguinal hernia only traverses the lower part of the inguinal canal. It pushes before it or bursts through that part of the posterior wall of the canal which forms the floor of Hesselbach's triangle, and, having thus gained the interior of the canal by a short cut, it emerges like the oblique variety at the external abdominal ring.

The deep epigastric artery bears a different relation to each of these forms of hernia. This vessel lies close to the inner margin of the internal abdominal ring, and it forms the outer boundary of Hesselbach's triangle; consequently, in oblique inguinal hernia, the protrusion, as it enters the inguinal canal, lies external to the vessel, whilst, in direct inguinal hernia, it lies internal to it. So important are these relations, that the terms external and internal are frequently employed to denote the two forms of inguinal hernia instead of oblique and direct.

It is also essential that the student should determine the relation which these forms of hernia hold to the inguinal pouches of peritoneum.

In oblique inguinal hernia the protrusion invariably leaves the abdominal cavity at the lower and inner part of the external inguinal pouch. It is here that the internal abdominal ring is situated.

In the case of direct inguinal hernia the protrusion may leave the abdominal cavity either from the middle or from the internal inguinal pouch, both of which are in relation to the floor of Hesselbach's triangle. In almost every case a hernial protrusion in passing to the surface carries before it a portion of the parietal peritoneum, which constitutes its immediate covering, and is termed by surgeons the sac of the hernia (Fig. 96 left side). In oblique inguinal hernia the other coverings which the protrusion acquires are identical with those of the spermatic cord. Entering the internal abdominal ring, it receives an investment from the infundibuliform fascia; emerging from the lower border of

FIG. 96.-Diagram to show the different peritoneal relations in an ordinary inguinal hernia (left side) and a congenital inguinal hernia (right side).

the internal oblique, it acquires a cremasteric covering; and, coming out through the external abdominal ring, it obtains the external spermatic or intercolumnar fascia. From the surface, then, to the peritoneal sac, the following are the coverings of an oblique inguinal hernia :— 1. Skin and superficial fascia.

2. Intercolumnar or external spermatic fascia.

3. Cremasteric fascia.

4. Infundibuliform fascia.

5. Extra-peritoneal fatty tissue.

6. Parietal peritoneum, constituting the hernial sac.

In direct inguinal hernia the coverings of the protrusion differ according to the part of Hesselbach's triangle through which it projects. If the student examine the floor of this triangular area, he will observe that the conjoined tendon does not stretch over its entire extent; that,

towards the outer part of the space, the transversalis fascia alone forms the floor. When a direct hernia leaves the abdomen from the middle inguinal pouch, it is through this outer part of Hesselbach's triangle that it protrudes, and, in this case, the coverings are almost identical with those of oblique hernia.

1. Skin and superficial fascia.

2. Intercolumnar or external spermatic fascia.

3. Cremasteric fascia (as a general rule).

4. Transversalis fascia.

5. Extra-peritoneal fatty tissue.

6. Parietal peritoneum or sac.

This form of direct hernia is comparatively rare.

The more common

form of direct hernia leaves the abdomen from the internal inguinal pouch, and pushes its way through the inner part of Hesselbach's triangle. It therefore acquires a covering from the conjoined tendon. The following are its investments :

1. Skin and superficial fascia.

2. Intercolumnar or external spermatic fascia.

3. Conjoined tendon.

4. Transversalis fascia.

5. Extra-peritoneal fatty tissue.

6. Parietal peritoneum or hernial sac.

When the conjoined tendon is feeble, or when a direct hernia takes place suddenly, the protrusion may burst through it, in which case it does not obtain a covering from this source.

There are two special varieties of oblique inguinal hernia which it is necessary to mention—viz., congenital hernia and infantile hernia.

Congenital Hernia.—We have seen that the passage of the testicle from the abdomen into the scrotum is accompanied by a protrusion of parietal peritoneum, which lines the inguinal canal and the scrotal sac. This diverticulum is called the processus vaginalis. Under ordinary circumstances the lower part persists as the tunica vaginalis, whilst the upper part becomes obliterated so as to completely shut off the communication between the general peritoneal cavity and the cavity of the tunica vaginalis. In certain cases this closure fails to take place, and an open pathway from the peritoneal cavity into the processus vaginalis, is the result (Fig. 97, B.). Such a condition is favourable to the occurrence of a hernial protrusion into the open processus vaginalis, and a hernia of this nature is distinguished by the term congenital. (Fig. 96 right side).

Infantile Hernia. -The conditions favourable to the occurrence of an infantile hernia are also due to faults in the developmental process, by which the testicle acquires its serous investment. They may be said to owe their origin to an excess of zeal on the part of the gubernaculum. The processus vaginalis remains patent, or is only partially closed. The gubernacular tissue in relation to the parietal