peritoneum draws down into the inguinal canal a second test-tube-like diverticulum of the membrane behind the true processus vaginalis (Fig. 97, S.). This is altogether an abnormal peritoneal recess which is thus produced, and it gives rise to a dangerous condition, because at any time an abdominal content may be forced into it. When this takes place an infantile hernia is the result. Four varieties are recognised according to the state of the true processus vaginalis. These are indicated in the diagram (Fig. 97).

Femoral Hernia. -This consists in the protrusion of an abdominal

FIG. 97.-Diagram to illustrate the four different varieties of infantile hernia. (After Lockwood.)

A. Processus vaginalis closed above.

B. Processus vaginalis closed above and below, but open in intermediate

part.

P.V. Processus vaginalis.

T.V. Tunica vaginalis.

C. Processus vaginalis open throughout its entire extent.

D. Processus vaginalis closed below, but open above.

T. Testicle.

S. Hernial sac.

content from the abdominal cavity into the region of the thigh. In its descent it passes behind Poupart's ligament along the crural canal or innermost compartment of the femoral sheath. It is consequently mainly the duty of the student who is engaged in the dissection of the lower limb, and within whose domain the femoral sheath lies, to investigate the anatomical connections of this variety of hernia (p. 220).

Still it is essential that the dissector of the abdomen should examine, from its abdominal aspect, the crural ring or aperture of communication between the crural canal and the abdominal cavity, and give the dissector of the lower limb an opportunity of doing so likewise.

A

The crural ring is placed immediately behind Poupart's ligament, in the interval between the external iliac vein and the base of Gimbernat's ligament. If the peritoneum is still in position at this point it may exhibit a slight digital depression as it passes over the ring. Strip the peritoneum from the greater part of the iliac fossa. The extraperitoneal fatty tissue, which stretches over the crural ring, will be observed to be denser, stronger, and more fibrous than elsewhere. special name is applied to this small portion of the extra-peritoneal fatty tissue. Seeing that it is applied to the ring in such a manner as to close the crural canal at its abdominal end, it is called the septum crurale. The extra-peritoneal fatty tissue should now be dissected back with the handle of the knife, to the same extent as the peritoneum. The fascia iliaca clothing the iliacus and psoas muscles is thus exposed, and the dissector should note that the external iliac vessels lie upon and not behind this fascia.

The student is now in a position to study the manner in which the crural ring is formed. Let him follow the fascia iliaca and the fascia transversalis towards Poupart's ligament. If the dissection has been carefully performed, he will observe that to the outer side of the external iliac vessels these two fascia become directly continuous with each other, and, further, that along the line of union they are both firmly attached to Poupart's ligament. It is evident, then, that no hernial protrusion could leave the abdominal cavity behind Poupart's ligament and external to the iliac vessels.

Opposite the iliac vessels the arrangement of the fascia will be found to be very different. Here the fascia iliaca is carried downwards behind the vessels, whilst the fascia transversalis is prolonged downwards in front of the vessels and behind Poupart's ligament. In the region of the thigh they together constitute a funnel-shaped sheath for the femoral artery and vein, and for some lymphatics ascending to the abdomen. This sheath is divided into three compartments by two vertical partitions. The femoral artery occupies the outermost compartment, and the vein the middle compartment, whilst the innermost compartment, called the crural canal, is occupied by the lymphatics, and sometimes by a small lymphatic gland.

An essential difference between these compartments is this—that whilst the two outer are completely filled up by the artery and vein, the crural canal is much wider than is necessary for the passage of its contents. Gauge the width of the crural ring by introducing the point of the little finger. It is readily admitted within the opening. Here, then, is a source of weakness to the abdominal wall, and one which is greater in the female than in the male, seeing that the distance between the iliac and pubic spines is proportionally greater, and, in consequence, the crural ring wider.

When the finger is within the ring, mark the structures which surround it-in front, Poupart's ligament, with the spermatic cord or round ligament of the uterus; behind, the ramus of the pubis, giving origin to the pectineus muscle, which is covered by the pubic portion of the fascia lata; internally, the sharp crescentic free border of Gimbernat's ligament; and externally, the external iliac vein.

It is still more necessary to note the relations of the blood-vessels to the crural ring. The external iliac vein has been seen to lie to its outer side. The deep epigastric artery, as it ascends on the posterior aspect of the abdominal wall, is close to its upper and outer margin, and sends its pubic branch inwards in front of it. More important than

any of these is the relation of the obturator artery, when it takes origin from the deep epigastric. This anomalous vessel may adopt one of three courses (1) It may follow the course of the pubic artery, an enlarged form of which it in reality is, and pass inwards in front of the ring, and then descend along its inner margin. In this case, the ring is surrounded on all sides, except posteriorly, by important vessels. (2) It may pass downwards and backwards across the crural ring. (3) It may run downwards between the ring and the external iliac vein (vide p. 221).

Internal to the crural sheath the passage of a hernia protrusion behind Poupart's ligament is effectually prevented by Gimbernat's ligament.

Femoral hernia is more common in females, and inguinal hernia in males; and for the very evident reason, that in the female the crural canal is relatively larger, whilst in the male the passage of the spermatic cord weakens the inguinal region more than the passage of the small round ligament of the uterus.

Umbilical Hernia. This form of hernia consists in the protrusion of an abdominal content through the umbilical ring in the linea alba. When it occurs in the foetus the hernia passes into the umbilical cord, and the three vessels are separated by it. More than one case has occurred in which the bowel has been cut in dividing the cord at the birth of the child. In the adult the fibrous cords in connection with the umbilicus are related to the lower border of the ring, and the hernia escapes through its upper part (Treves).

The Penis. The penis has already, to a certain extent, been studied in the dissection of the perineum (p. 349). It has been seen to be composed of the two corpora cavernosa and the corpus spongiosum. Posteriorly, the corpora cavernosa separate from each other, become tapered and are attached to the sides of the pubic arch under the name of the crura penis; anteriorly, they together form a blunt rounded extremity, which is covered by the glans penis.

The corpus spongiosum, when traced backwards into the perineum, expands into the bulb of the penis, which is attached, in the mesial plane, to the anterior aspect of the triangular ligament; traced forwards to the extremity of the penis, it is again found to expand into the glans penis, which fits like a cap upon the rounded ends of the corpora cavernosa. The glans penis is somewhat conical in shape, and the projecting margin of its base is termed the corona glandis. The urethra opens at the extremity of the glans by a vertical fissure, called the meatus urinarius.

The integument of the penis is remarkable for its great delicacy and elasticity, and the absence of hairs. It has a brownish tint, and is freely movable over the organ. At the glans the skin leaves the body of the penis, and, passing for a variable distance over the glans, is folded back upon itself so as to form the prepuce. The deep layer of the prepuce reaches the penis again behind the corona glandis, and is then reflected forwards over the glans to become continuous with the mucous membrane of the urethra at the meatus urinarius. A slight fold will be observed on the under surface of the glans, extending from the lower angle of the urinary orifice to the prepuce; this is the frænum preputii.

Dissection.-Reflect the integument from the surface of the penis by making a longitudinal incision along the middle line of the dorsum. The superficial fascia will then be seen to be composed of a quantity of loose areolar tissue. We never find fat in the meshes of this tissue. The suspensory ligament and the dorsal vessels and nerves of the penis should now be dissected.

Suspensory Ligament.-The suspensory ligament is a strong fibro-elastic band of a triangular shape. By its posterior border it is attached to the symphysis pubis. Towards the penis it separates into two lamellæ, which join the body of the organ, and between which are placed the dorsal vessels and nerves.

Dorsal Vessels and Nerves.-On the dorsum of the penis, in the groove which extends along the middle line between the two corpora cavernosa, is the dorsal vein; on each side

of this is the dorsal artery, and superficial and external to the artery is the dorsal nerve. On the dorsum of the penis, therefore, we find one vein, two arteries, and two

nerves.

The dorsal vein of the penis begins by several twigs from the glans and prepuce. It extends backwards in the middle line, and disappears between the two layers of the suspensory ligament. It gains the pelvis by passing under the sub-pubic ligament, and ends by joining the prostatic plexus of veins.

The dorsal arteries are the terminal twigs of the internal pudic vessels. Piercing the triangular ligament, they pass forward between the two layers of the suspensory ligament, and, continuing their course on the dorsum of the penis, they terminate in branches for the glans penis.

The dorsal nerves are branches of the internal pudic. They have a similar course to the arteries, and end in fine twigs to the papillæ of the glans.

ABDOMINAL CAVITY.

The abdominal cavity may now be opened completely by carrying an incision from the umbilicus upwards to the ensiform cartilage. On throwing the two flaps thus formed upwards and outwards over the lower margin of the thorax, a strong fibrous cord, the obliterated umbilical vein, will be observed extending from the umbilicus to the under surface of the liver. The obliterated umbilical vein also receives the name of the round ligament, or ligamentum teres, of the liver. As it ascends towards that organ, it gradually recedes from the posterior surface of the anterior abdominal wall, taking with it a fold of peritoneum, termed the falciform ligament of the liver.

Shape and Boundaries of the Abdominal Cavity.—The abdominal cavity is ovoid in shape, its vertical diameter being the longest. Superiorly, it is roofed by the dome