Page:Laboratory Manual of the Anatomy of the Rat (Hunt 1924).djvu/60

46 seters on the lower jaw. Locate its origin on the skull and its insertion on the mandibles at, and near, the symphysis.

Sternahyoideus Muscle. The two sternohyoideus muscles lie on the ventral side of the neck behind the digastricus. They are in contact with one another along the sagittal plane of the neck. Origin, the sternum. Insertion, the hyoid bone.

The sternomastoideus and clavotrapezius muscles have already been mentioned in connection with the lateral view. Identify them here.

Omohyoideus Muscle. This muscle will be observed on the ventral surface of the neck in the triangular space bounded by the digastricus, sternohyoideus, and sternomastoideus muscles. Origin, the superior margin of the scapula. Insertion, the hyoid bone.

The Pectoral Muscles are a prominent group on the ventral side of the thorax. The pectoralis major partially conceals the pectoralis minor. The pectoralis major consists of a superficial and a deeper portion. The origin of the superficial portion is the anterior half of the sternum's manubrium; it is inserted on the deltoid ridge. The deeper portion originates on the manubrium of the sternum and the first and second sternebrae; the insertion is likewise on the deltoid ridge.

Pectoralis Minor Muscle. Remove the pectoralis major to study this muscle. It comprises three parts. The origin of the first, or most anterior, part is the second to the fifth sternebrae, inclusive; insertion, on the coracoid process of the scapula and the lesser tuberosity of the humerus. The second, or middle, portion originates at the fifth sternebra and is inserted on the deltoid ridge. The origin of the third portion is the xiphoid process of the sternum; the insertion is on the coracoid process of the scapula.

Rectus Abdominis Muscle. This consists of a pair of