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 vertebrse 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 



[Suhdorso-atloideus.) 



(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 the first 

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

 six posterior cervical vertebrse. 



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 vertebrae. The dorsal portion is related with 

 the pleura and sympathetic nerves. 



