The rectus abdominis is covered, in its anterior portion, by the sterno-trochinian muscle (posterior segment of the small pectoral). In contracting, this muscle brings the chest nearer the pelvis, and as a result flexes the vertebral column. It also contributes to the compression of the abdominal viscera. =Pyramidalis Abdominis.=--This unimportant little muscle, which in man is situated at the lower part of the abdomen, extends from the pubis to the _linea alba_. It is not present in the domestic animals. We consider it interesting, however, to point out, although the fact is not a very useful one as regards external form, that this muscle is distinctly developed in marsupials. We know that in the opossum, the kangaroo, and the phalanger fox, the young are brought forth in an entirely incomplete state of development, and that, during a certain period, they are obliged to lodge in a pouch which is placed at the lower part of the abdomen of the mother. Now, this pouch contains the mammary glands; but the young, being too feeble to exercise the requisite suction, the pyramidal muscles come to their assistance. These muscles, in contracting, approximate to one another two bones which are placed above the pubis, the (so-called) marsupial bones (see Fig. 80); by their approximation the bones in question, which are placed behind and on the outer side of the mammary glands, compress the latter, and thus is brought about the result which the little ones, on account of their feebleness, would, without that intervention, be incapable of obtaining for themselves. Muscles of the Back =Trapezius= (Fig. 68, 1, 2; Fig. 69, 1, 2; Fig. 70, 1, 2).--This muscle, more or less well developed, according to the species, is divided into two portions, of which the names indicate the respective situations--a cervical and a dorsal. These two parts, considered in the order in which we find them, take their origin from the superior cervical ligament and from the spinous processes of the first dorsal vertebræ. From these different points the fibres are directed towards the shoulder; the anterior are, consequently, oblique downwards and backwards, and the posterior are directed downwards and forwards. They are inserted into the scapula in the following manner: the fibres of the dorsal portion are attached to the tuberosity of the spine; those of the cervical region are also fixed into the same spine, but into a considerably larger surface.