. The anatomy of the domestic animals. Veterinary anatomy. 278 AND IICSCLES OF THE HORSE Acting together, they may assist in extending the spine, acting singly in inclining it laterally. Structwe.—This muscle presents a distinct segmental arrangement. It is composed of a series of bundles, the fibers of which are directed forward and a little ventro-laterally. From these are detached two sets of tendons. The superficial tendons spring from the lateral edge of the muscle. They are flat and are about half an inch in width. Each crosses two or three intercostal spaces, to be inserted on t
. The anatomy of the domestic animals. Veterinary anatomy. 278 AND IICSCLES OF THE HORSE Acting together, they may assist in extending the spine, acting singly in inclining it laterally. Structwe.—This muscle presents a distinct segmental arrangement. It is composed of a series of bundles, the fibers of which are directed forward and a little ventro-laterally. From these are detached two sets of tendons. The superficial tendons spring from the lateral edge of the muscle. They are flat and are about half an inch in width. Each crosses two or three intercostal spaces, to be inserted on the posterior border of a rib. The deep tendons are detached from the dorsal part of the deep face of the muscle. Each passes backward across one or two inter- costal spaces to its origin on the anterior border or lateral surface of a rib. Small bursse may be found between the ribs and tendons. Relations.—Superficially, the dorsal and ventral serrati; deeply, the external inter- costals and the ribs. The lumbar origin is covered by the longissimus dorsi. The deep cervical and dorsal vessels cross the surface of the muscle at the first and second intercostal spaces respectively, and branches of the in- tercostal vessels and nerves emerge between it and the longissimus dorsi; here a fascial layer dips in between the two. Blood-supply.—Intercostal arteries. ^^ „ ., , n 4 1 \\\ Nerve-supply.—Dorsal branches of the ^^^ZI^ r w>A ' ** \l\ thoracic nerves. 7. Longissimus dorsi.'—This is the largest and longest muscle in the body. It extends from the sacrum and ilium to the neck, filling up the space between the spinous processes medially and the lumbar trans- verse processes and the upper ends of the ribs ventralh'; consequently it has the form of a three-sided prism. Origin.—(1) The tubera, crest, and ad- jacent part of the ventral surface of the ilium; (2) the first three sacral spines; (3) the lum- bar and thoracic spines and the supraspinous ligament. Insertion.—(
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