Part 31

Relations.—Internally, with the ribs.

Action.—If the scapula is fixed, it is a muscle of respiration.

=Teres et Infraspinatus= (Fig. 13, No. 11). Location.—Scapular region.

Origin.—From the superior surface and outer margin of the posterior two-thirds of the scapula.

Insertion.—The fibers pass forward and outward, and insert to the humerus at the middle of the ulnar margin of the pneumatic fossa, between the forks of the triceps.

Shape. —Flat, triangular-shaped.

Relations.—Anteriorly, with the supraspinatus. Internally, with the ribs.

Action.—Aids in keeping the humerus in its socket. Assists in closing the wing by drawing the humerus to the side of the body.

=Intercostales= (Fig. 24, No. 5). Location.—Between the ribs of the upper thoracic region.

Origin and Insertion.—From the anterior border of one rib, the fibers, passing obliquely upward and forward, and the lower portion downward and forward, are inserted to the posterior border of the rib just in front.

Shape.—They are best developed in the anterior portion of the thoracic region and extend down as far as the sternal ribs.

Relations.—Internally the pleura, and anteriorly and posteriorly the ribs.

Action.—The first rib being rendered fixed by the scalenus medius, the muscles draw the ribs forward, thus aiding inspiration.

=Levatores Costarum= (Fig. 24, No. 2). Location.—Supero-lateral portion of the thorax.

Origin and Insertion.—A series of muscles, the first of which extends from the extremity of the transverse process of the twelfth vertebra, the fibers passing downward and backward to the anterior free margin of the upper third of the long posterior rib, and to the external surface close to its margin. The others arise and insert in a similar manner from the ends of the diapophyses of all the dorsal vertebræ and attach to each succeeding rib. Those in front are best developed.

Shape.—Thin and triangular.

Relations.—External to the intercostales.

Action.—Aids in respiration.

=Appendico-costales= (Fig. 24, No. 1). Location.—The lateral side of the thorax.

Origin and Insertion.—From the posterior edge of an uncinate process or epineural appendage, the fibers extending downward and backward to the outer surface of the succeeding rib.

Shape.—A series of thin triangular-shaped muscles.

Relations.—Internally, with the intercostales.

Action.—Aids in respiration.

THE ANTERIOR PECTORAL GROUP

Tensor patagii longus Tensor patagii brevis

=Tensor Patagii Longus= (Fig. 15C, No. 1; Fig. 14, No. 2). Location.—Anterior shoulder region, in the triangular patagium of the wing.

Origin.—By a flat tendon common to it and the tensor patagii brevis from the supero-mesial line of the head of the clavicle.

Insertion.—By a long slender tendon extending in the duplicature of the patagium, with which the fibers blend. Passing to the side of the extensor metacarpi radialis longus, it extends over the end of the radius and is inserted to the os carpi radiale, and to the fascia which binds down the other tendons on the anterior part of the wrist-joint.