270 FASCIA AND MUSCLES OF THE HORSE 



Relations. — Ventrally, to the preceding muscle; dorsally, to the atlas, atlanto- 

 occipital articulation, and the basilar part of the occipital bone; laterally, to the 

 rectus capitis lateralis and the guttural pouch. 



Blood- supply . — Occipital artery. 



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



10. Rectus capitis lateralis. — This is a still smaller muscle, which lies for the 

 most part under the obliquus capitis anterior. 



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

 Insertion. — The paramastoid process of the* occipital bone. 

 Action. — The same as the preceding muscle. 

 Structure. — Fleshy. 



Relations. — Superficially, the obliquus capitis anterior, 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. 



11. Longus coUi. — This muscle covers the ventral surfaces of the vertebrae, 

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

 two parts, thoracic and cervical. 



Origin. — (1) Thoracic part, the bodies of the first six thoracic vertebrae; (2) 

 cervical part, the transverse processes of the cervical vertebrae. 



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

 two cervical vertebrae; (2) cervical part, the bodies of the cervical vertebrae and 

 the ventral tubercle 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 ten- 

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

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

 transverse process of one vertebra forward and mediallj' to its insertion into a ver- 

 tebra further forward. The most anterior bundle 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 oesophagus; dorsally, 

 the vertebrae and the costo-vertebral joints; laterally, the dorsal, deep 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 the neck, the intertransversales muscles; lat- 

 erally, the scalenus, the rectus capitis ventralis major, and the intertransversales 

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

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



Blood-supply. — Subcostal and vertebral arteries. 



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



12. 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 ven- 

 tral part. 



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

 process; the ventral bundles extend between adjacent transverse processes. 

 Action. — To flex the neck laterally. 

 Structure. — They contain strong tendinous intersections. 

 Relations. — Superficially, the brachiocephalicus, rectus capitis ventralis ma- 



