THE ABDOMINAL WALL
The construction of the abdominal wall follows the common pattern in its essential features. The cutaneous muscle of the trunk is extensive as well as thick ventrally where it passes through the flank fold.
It leaves the abdominal floor uncovered, except for cranial (and inconstant caudal) preputial muscles. The deep fascia is without the elastic component that in the larger species imparts the characteristic yellow color. The three muscles of the flank show few distinctions of importance, and because surgical experience has shown that their fleshy parts tend not to hold sutures well, attention can be concentrated on the aponeuroses. The site favored for laparotomy is an almost wholly tendinous strip, about 10 cm long and barely 5 cm wide, situated along the lateral edge of the rectus muscle and deep to the flank fold.The alternation of the abdominal muscles with layers of fat accounts for the characteristic appearance of the bacon rasher.
Umbilical hernias used to be common in this species. If a satisfactory closure of these defects is to be obtained in the abdominal wall, it is first necessary to reflect the cranial part of the prepuce. This exposes the wide part of the linea alba that alone provides sufficient breadth of tissue to allow overlapping and suture of the margins of the hernia ring.
The other region of practical interest is provided by the inguinal canal. In principle, this conforms to the general arrangement: it is a potential space between the two oblique muscles (for details see Figure 34-2). The deep ring, the entry to the canal, is found between the caudal border of the internal oblique and the aponeurosis of the external oblique (see Figure 2-27). The superficial opening is the split in the external aponeurosis that defines its division into pelvic and abdominal parts. The caudal part of the canal is very short, but it widens cranially as the result of the divergent orientations of the deep and superficial inguinal rings: the deep ring is angled craniodorsally, while the superficial ring is angled slightly ventrally as well as cranially. Anomalies of gubernacular development are common in pigs; if the canal is dilated (Figure 34-3), they are predisposed to inguinal hernia. The hernia generally takes the form of a loop of small intestine that stretches the vaginal ring and forces a passage into the tunica vaginalis, which raises a subcutaneous swelling between the thighs. These hernias make castration of affected animals requiring attention.