_Relations._—Externally, with the depressor coccygis. _Action._—Singly, pulls the tail downward and outward; with its fellow, pulls the tail downward. =Depressor Coccygis.= _Location._—The outermost of the infero-lateral muscles of the tail. _Origin._—From the lower half of the posterior margin of the ischium and the anterior three-fourths of the posterior margin of the post-pubic element of the pelvis beyond it. _Insertion._—To the thickened rim of the inferior and expanded portion of the pygostyle. _Shape._—Flat, triangular. _Relations._—Internally with the depressor caudæ. _Action._—Singly, pulls the tail downward and to one side; with its fellow, pulls the tail downward. =Lateralis Caudæ= (Fig. 23, No. 5). _Location._—The lateral side of the tail. _Origin._—From the tip of the transverse process of the first free caudal vertebræ. _Insertion._—To the outer three quill butts of the main tail feathers. _Shape._—Four fasciculi forming a fleshy belly. _Relations._—Inferiorly, with the levator caudæ and superiorly with the depressor caudæ. _Action._—Singly, pulls the tail downward and outward; with its fellow, pulls the tail downward. The outermost fasciculus contracting, spreads the tail feathers. =Lateralis Coccygis= (Fig. 25, No. _E_, 2). _Location._—The infero-lateral side of the caudal vertebræ. _Origin._—From the surface of the posterior end of the ilium and by tendons from the under side of the ends of the first three or four caudal vertebræ. _Insertion._—To the side of the posterior margin of the expanded portion of the pygostyle. _Shape._—Subcompressed mass. _Relations._—With the transverse processes of the caudal vertebra, inferiorly. _Action._—Controls the lateral movements of the tail and its feathers, and the oblique downward movement. =Infracoccygis= (Fig. 25, No. _E_, 1). _Location._—The extreme inferior portion of the caudal vertebræ. _Origin._—From the inferior surface of the diapophysis of the last vertebra which anchyloses with the pelvic sacrum, and from all the free caudal vertebræ. _Insertion._—Into the lower side of the pygostyle. _Shape._—Flat, somewhat triangular. _Relations._—Superiorly, with the vertebræ, laterally, with the lateralis coccygis, and mesially, with its fellow of the opposite side. _Action._—Depresses the tail. THE COSTAL REGION Latissimus dorsi Trapezius Rhomboideus Serratus magnus anticus Serratus parvus anticus Teres et infraspinatus Intercostales Levatores costarum Appendico-costales =Latissimus Dorsi= (Fig. 24, No. 7). _Location._—Supero-lateral portion of the dorsal region.