When the panniculus carnosus is removed, a broad sheet of yellow elastic tissue is exposed, spread over the under surface and sides of the abdomen, to which the term "abdominal tunic" is given. This elastic layer is thick behind, and gradually thins as it passes forwards and upwards over the sides of the belly.
Posteriorly it divides and gives a layer to the sheath, which it supports as in a sling. In the stallion this segment is of considerable thickness, and assists in sustaining the penis when in a state of erection. It is known as the " suspensory ligament of the sheath ".
In the female a similar division takes place, by which each milk-gland becomes invested in an elastic capsule. Generally considered, the abdominal tunic supplies a large bandage, which braces up the abdominal muscles and enables them to support the weight of the organs contained in the belly. In old brood mares it is of considerable thickness, owing to the additional weight imposed upon the walls of the belly during a succession of pregnancies.
The three first named possess broad, aponeurotic tendons, all of which converge towards the centre of the belly and intermix their fibres, as a result of which a dense white band is formed, extending from the pubis behind to the sternum in front. This band is termed "linea alba" or white line. A little behind the middle of this line a lozenge-shaped space appears, in which the umbilical oponing or navel originally existed.