Regional Variation in the Histomorphology and Tensile Strength of the Ventral Rectus Sheath in the Male Goat (Capra Hircus)

The ventral rectus sheath (VRS) plays a key role in the stabilization of the ventral abdominal wall. This sheath has to be particularly strong in ruminants to accommodate the viscera and the large quantities of forage in their stomach. This study was conducted to establish the structural and the mechanical properties of the ventral rectus sheath in the goat, a browser, in order to elucidate its function. The ventral rectus sheath was formed by superficial and deep lamina consisting of obliquely aligned collagen fibers derived from the external and internal oblique abdominal aponeuroses respectively. Closely apposed and intimately held to the superficial lamina was a layer of longitudinally aligned elastic fibers, the ttunica flava abdominis or modified deep fascia. This tunica flava abdominis progressively increased in thickness from the epigastrium to the hypogastrium. On tensiometry, the epigastric ventral rectus sheath withstood about half the load (50N/mm2) required to reach yield point compared to the umbilical ventral rectus sheath (94.5N/mm2). Furthermore, the Youngs modulus showed that the umbilical ventral rectus sheath was the stiffest at 669 (SD 22.2) N/mm2 while the epigastric ventral rectus sheath was the weakest at 554 (SD 29) N/mm2 respectively when exposed to longitudinal traction. In conclusion, the progressively thickening of the tunica flava abdominis and the superficial lamina from the epigastrium to the hypogastrium may confer reversible stretch ability and strength to the ventral rectus sheath and is therefore well suited for longitudinal load strength needed to support the compound stomach during browzing.