Page:Laboratory Manual of the Anatomy of the Rat (Hunt 1924).djvu/58

44 Triceps Brachii Muscle. This muscle has three heads—the caput longum, caput laterale, and caput mediale.

Caput longum. This head lies on the dorsal side of the upper arm. Origin, the anterior third of the axillary margin of the scapula. Insertion, the olecranon.

Caput laterale. This head lies on the lateral surface of the upper arm. Origin, the larger tubercle of the humerus. Insertion, the olecranon.

Caput mediale. It lies along the dorsal surface of the humerus. It is wedge-shaped, being pointed at the anterior end, but greatly increasing in size posteriorly. Origin, the dorsal and dorsolateral surfaces of the humerus throughout practically the whole ventral surface of the muscle. The pointed anterior end of the muscle reaches nearly to the head of the humerus. Insertion, the olecranon. The caput mediale is not seen superficially, but is found when the caput laterale and caput longum are removed.

External Oblique Muscle. This is a very extensive thin muscle situated laterally and ventrally on the thorax and abdomen. Anterior origin: it is attached along the side of the thorax by a muscular slip to each rib from the fourth to the twelfth. Posterior origin, the lumbodorsal fascia. The anterior slips interdigitate with the posterior slips of the serratus anterior. Insertion: (1) it fastens to a fascia on the ventral surface of the thorax and abdomen; (2) is attached along the whole length of the inguinal ligament (a white, stout, slender ligament extending along the angle between the inner surfaces of the hip and body, from the symphysis pubis to the crest of the ilium); (3) a broad branch of the muscle extends back to the symphysis pubis. Carefully expose all parts of the origins and insertions and determine the muscle's probable action by an inspection of its relations.