238 FASCIiE AND MUSCLES OF THE HORSE 



8. Multifidus dorsi (semispinalis of the back and loins). — This is a long 

 segmental muscle which covers the sides of the spinous processes of the vertebrae 

 from the sacrum to the neck. 



Origin. — (1) The lateral portion of the sacrum; (2) the articular processes of 

 the lumbar vertebrae; (3) the transverse processes of the thoracic vertebrce. 



Insertion. — The spinous processes of the first two sacral, the lumbar, thoracic, 

 and last cervical vertebrce. 



Action. — -Acting with its fellow, it is an extensor of the spine; acting singly, 

 it flexes it laterally. 



Structure. — It is composed of a series of bundles which are directed obliquely 

 forward and upward. Each fasciculus passes over several vertebrae to its insertion. 

 In the posterior part of the series the bundles cross two or three vertebrae and are 

 inserted into the summits of the spines. Anteriorly, the bundles have a more 

 horizontal direction, cross three to five vertel^rae, and are inserted into the sides 

 of the spines considerably below their summits. A further complication consists 

 in the fusion of several bundles into a common insertion. 



Relations. — Superficially, the longissimus; deeply, the vertebral spines. 



Blood-supply. — Intercostal and lumbar arteries. 



Nerve-supply. — Dorsal branches of the thoracic and lumbar nerves. 



9. Intertransversales lumborum. — These are very thin muscular and tendin- 

 ous strata, which occupy the spaces between the transverse processes of the lumbar 

 vertebrae except the fifth and sixth. 



Action. — To assist in flexing the loins laterally. 



Relations. — Superficially, the longissimus; deeply, the quadratus lumborum. 



Blood-supply. — Lumbar arteries. 



Nerve-supply. — Lumbar nerves. 



The Fascia and Muscles of the Tail 



The muscles of the tail are inclosed in the strong coccygeal fascia, which is 

 continuous in front with the gluteal fascia and blends with the lateral sacro- 

 iliac ligament. At the root of the tail it is loosely attached to the subjacent muscles, 

 but further back it is intimately adherent to them. From its deep face are de- 

 tached septa which pass between the muscles to become attached to the vertebrae. 



1. Coccygeus (Compressor coccygis; ischio-coccygeus). — This is a |flat, 

 triangular muscle which lies chiefly between the sacro-sciatic ligament and the 

 rectum. 



Origin. — The pelvic surface of the sacro-sciatic ligament near the ischiatic 

 spine. 



Insertion.— The first four coccygeal vertebrae and the coccygeal fascia. 



Action. — -Acting together, to depress (flex) the tail, compressing it over the 

 perineum; acting singly, to depress and incline it to the same side. 



Structure. — -The origin of the muscle is aponeurotic. Becoming fleshy, its 

 fibers pass upward and backward and divide into two layers. The outer layer is 

 attached to the vertebrae, the inner to the fascia; included between the two lie 

 the intertransversales. When the tail is raised, the ventral edges of the muscles 

 produce a distinct ridge at either side of the anus. 



Relations. — Outwardly, the sacro-sciatic ligament and the semimembranosus; 

 inwardly, the rectum and the sacro-coccygeus ventralis muscle. The internal 

 pudic arter}' crosses the outer face of the origin of the muscle. 



2. Sacro-coccygeus superior (M. sacrococcygeus dorsalis medialis; erector 

 s. extensor coccygis). — This muscle lies along the dorso-median aspect of the 

 tail, in contact with its fellow. 



Origin. — The last three sacral spines and some of the coccygeal spines. 



