228 FASCL-E AND MUSCLES OF THE HORSE 



Insertion. — The basilar process, close to the preceding muscle. 



Action. — To flex the occipito-atlantal articulation. 



Structure. — Fleshy. 



Relations. — Below, to the preceding muscle; above, to the atlas, occipito- 

 atlantal articulation, and the basilar process; externally, to the rectus capitis 

 lateralis and the guttural pouch. 



Blood-supply. — Occipital artery. 



Nerve-supply. — Ventral branch of the first cervical nerve. 



9. Rectus capitis lateralis. — This is a still smaller, entirely fleshy muscle, 

 which lies for the most part under the small oblique muscle. 



Origin. — The atlas, external to the preceding muscle. 

 Insertion. — The paramastoid or styloid process of the occipital bone. 

 Action. — -The same as the preceding muscle. 

 Structure. — ^Fleshy. 



Relations. — Superficially, the small ol)liciue muscle, the occipital vessels, and 

 the ventral branch of the first cervical nerve. 

 Blood-supply. — Occipital artery. 

 Nerve-supply. — Ventral branch of the first cervical nerve. 



10. Longus colli. — This muscle covers the ventral surface of the vertebrae, 

 from the sixth thoracic to the atlas, and is united with its fellow. It consists of 

 two portions, thoracic and cervical. 



Origin. — (1) Thoracic portion, the bodies of the first six thoracic vertebra?; 

 (2) cervical portion, the transverse processes of the cervical vertebrae. 



Insertion. — (1) Thoracic portion, the bodies and transverse processes of the 

 last two cervical vertebrae; (2) cervical portion, the bodies of the cervical vertebrae 

 and the tubercle on the ventral surface of the atlas. 



Action. — To flex the neck. 



Structure. — The muscle is composed of a succession of bundles. The largest 

 of these constitute the thoracic part of the muscle, which has a strong tendon in- 

 serted into the last two cervical vertebrae. A bursa is interposed between the tendon 

 and the spine at the first costo-vertebral articulation. The cervical portion con- 

 sists of a number of smaller bundles, each of which passes from its origin on the 

 transverse process of one vertebra forward and inward to its insertion into a vertebra 

 further forward. The most anterior l)undle is inserted by a strong tendon into 

 the ventral tubercle of the atlas. 



Relations. — The principal relations of the two muscles in the thorax are: 

 ventrally, the pleura, and, further forward, the trachea and a?sophagus; dorsally, 

 the vertebrae and the costo-vertebral joints; laterally, the dorsal, superior cervical, 

 and vertebral vessels, the sympathetic nerve, and the thoracic roots of the brachial 

 plexus. In the neck, important relations are : ventrally, the trachea and oesophagus, 

 the carotid artery, the vagus, sympathetic and recurrent nerves; dorsally, the 

 vertebrae and, in the middle third of tlu^ neck, the intertransversales muscles; 

 laterally, the scalenus, the rectus capitis anticus major, and the intertransversales 

 (in the anterior third). The terminal part of the muscle is separated from the 

 trachea by the resophagus, which is here median in position. 



Blood-supply. — Subcostal and vertebral arteries. 



Nerve-supply. -Ventral branches of the spinal nerves. 



11. Intertransversales colli (Mm. intertransversarii cervicis). — These are six 

 fasciculi which occupy the spaces between the lateral aspects of the vertebrae and 

 the transverse and articular processes. There is thus a bundle for each inter- 

 vertebral articulation except the first. Each bundle consists of a dorsal and 

 ventral portion. 



Attachments. — The dorsal bundles pass from transverse process to articular 

 process; the ventral bundles extend between adjacent transverse processes. 



