182 MYOLOGY. 



intersections. The anterior portion is the larger, flat from side 

 to side, and thin in front. 



Origin of the Anterior Portion. — From the transverse pro- 

 cesses of the last four cervical vertebra by short fleshy fasciculi. 



Insertion. — The anterior and outer border of the first rib. 



Origin of the Posterior Portion. — From the transverse pro- 

 cesses of the last three or four cervical vertebrae. 



Insertion. — To the superior part of the first rib. 



Relation. — Superiorly with the intertransversalis colli; inferiorly 

 with the sterno-maxillaris ; externally with the levator humeri, 

 pectoralis parvus, and subscapulo-hyoideus ; internally with the 

 trachea and carotid artery, and on the left side with the oesopha- 

 gus. Across its inferior border runs the jugular vein, and 

 between its anterior and posterior portions pass the nerves of the 

 brachial plexus. 



Action. — When the first rib is fixed, together these muscles 

 extend the neck ; acting singly, each turns it to one side. When 

 the neck is fixed, by drawing the first rib forward and supporting 

 it, it acts as an inspiratory muscle. 



LONGUS COLLI. 



(Subdorso-atloidevs.) 



(Fig. 75. a.) 



In the horse this is a single muscle, situated under the centra 

 of the cervical and anterior dorsal vertebrae. The dorsal portion 

 is fleshy, the cervical being made up of smaller fasciculi, con- 

 voluted and intersected by tendinous fibres. The fasciculi run 

 inwards and forwards. 



Origin. — From the inferior surface of the centra of ther first 

 six dorsal, and the inferior spines and transverse processes of the 

 six posterior cervical vertebrae. 



Insertion. — By a strong tendon to the inferior spine or 

 tubercle of the atlas ; it is also strongly attached to the second 

 cervical segment. 



Relation. — Externally and anteriorly with the rectus capitis 

 anticus major ; externally and posteriorly with the scalenus ; 

 inferiorly with the trachea, oesophagus, blood-vessels, and nerves ; 

 superiorly with the vertebroB. The dorsal portion is related with v 

 the pleura and sympathetic nerves. 



