_Origin._—In an attenuated fascia from the crest of the neural spines of the first, the second, and the third dorsal vertebræ. _Insertion._—To the skin in a broad pale stratum, over the scapular region. _Shape._—Thin, pale, and very delicate. _Relations._—Superiorly with the skin, and inferiorly with the shoulder. _Action._—Controls the skin of the region. =Dermo-iliacus.= _Location._—Along the back on either side of the spine. _Origin._—From the inner angle of the marginal portion of the antero-dorsal border of the ilium. _Insertion._—Passing forward as a delicate band it spreads out and becomes lost in the skin of the shoulder region. _Shape._—Thin, delicate, and ribbon-shaped. _Relations._—Superiorly with the skin. _Action._—If the posterior end is fixed, it will cause the feathers to lie close to the skin. Its action would then be opposite to the dermo-dorsalis. =Dermo-ulnaris.= _Location._—Outer surface of the anterior upper costal and the posterior humeral region. _Origin._—By a thin fascia from the outer part of the third and the fourth true ribs at the base of their epineural appendages. Also from the fascia between them. _Insertion._—The fibers pass forward and upward as a thick muscular bundle and is loosely attached to the skin at a point just back of the humerus. The tendon later becomes spread out and attached to the fascia as far as the elbow-joint. It covers the olecranon of the ulna. _Shape._—At first rather thick, fascicular-like; later becomes tendinous; and at its attachment it becomes spread out over the olecranon. _Relation._—Inferiorly with the ribs and humerus, and externally with the skin. _Action._—A depressor of the humeral region. THE SKELETAL MUSCLES THE MUSCLES OF THE HEAD Temporal Masseter Biventer maxillæ Entotympanicus Pterygoideus internus Pterygoideus externus Digastricus =Temporal= (Fig. 19, No. 4). _Location._—Occupies the temporal fossa. _Origin._—From the mesian line of the sphenotic process, and the adjacent wall of the orbit. _Insertion._—The fibers passing downward and forward blend with the fibers of the masseter. Inferiorly it inserts by a tendon to the coranoid process upon the superior ramal margin of the mandible. _Shape._—Fan-shaped with broad portion uppermost. _Relations._—It occupies the temporal fossa. It is related superiorly with the dermo-temporalis and skin. Inferiorly, with the biventer maxillæ and the masseter. _Action._—It aids in closing the jaw. =Masseter= (Fig. 19, No. 1). _Location._—Occupies the supero-lateral portion of the surface of the lower jaw.