Page:Laboratory Manual of the Anatomy of the Rat (Hunt 1924).djvu/57

Rh clavicle. Insertion, the lateral part of the crest that runs dorsally from the external auditory meatus.

Sternomastoideus Muscle. This muscle is anterior, and parallel to, the clavotrapezius. Origin, the anterior end of the manubrium. Insertion, by a tendon to the mastoid bone.

Spinotrapezius Muscle. Origin, (1) the spines of the fourth to the thirteenth thoracic vertebrae; (2) from the lumbodorsal fascia from the level of the thirteenth thoracic to the third lumbar vertebra. Insertion, the scapular spine. It draws the scapula dorsocaudad.

Latissimus Dorsi Muscle. This is a triangular muscle attached at one of its angles to the medial side of the humerus. Origin: the spines of the thoracic vertebrae from the eighth to the twelfth, inclusive, and the lumbodorsal fascia to the level of the third lumbar vertebra. Insertion, by a strong tendon to the medial surface of the humerus. It is also strongly united to the muscles lateral to it in the axillary region. The fibers converge to the tendon of insertion. It pulls the arm caudodorsad.

Acromiodeltoideus Muscle. Origin, the acromion and metacromion processes of the scalpa, and the ventral border of the clavicle. Insertion, the deltoid process of the humerus. The acromiodeltoideus is bipinnate ; the fibers from the clavicle form an acute angle with those from the acromion and metacromion processes where these two groups of fibers join a connective tissue septum ventral to the humerus. This septum forms the connection of the muscle with the deltoid process.

Spinodeltoideus Muscle. Origin, the infraspinous fascia and anterior two-thirds of the spine of the scapula. Insertion: it is united ventrally by an aponeurosis with the free edge of the deltoid tuberosity of the humerus. It flexes the humerus and rotates it outward.