178 OUTLINES OF EQUINE ANATOMY. 



the pharyngeal muscles, and thyro-hoideus and crico-thy- 

 roideus, and then becoming purely sensory pierces the fora- 

 men beween the thyroid cornu and the wing of the thyroid,, 

 and supplies the lining mucous membrane. The carotid 

 artery in passing wp the neck along the lateral part of the 

 trachea gives branches to the oesophagus and other neigh- 

 bouring structures, but the only constant branch is one 

 which runs to the thyroid body, and which also sends off 

 a large branch, the laryngeal, to the larynx. Along the 

 under surface of the vertebrae runs Longus colli, which 

 anteriorly extends to the tubercle or inferior spinous pro- 

 cess of the atlas, and runs as far back as the sixth dorsal ver- 

 tebra, becoming attached to the under surface of the 

 bodies and transverse processes, and inferior spinous pro- 

 cesses (except sixth cervical) of all the intervening 

 vertebrae. It lies in contact with its fellow internally, and 

 its thoracic portion is covered by pleura and forms a some- 

 what remarkable prominent cylindrical muscular mass. On 

 its external surface posteriorly just in front of the first 

 rib we see the vertebral artery and vein in their course 

 between the canal through the sixth cervical transverse 

 process and the entrance to the thorax. With them runs 

 a nerve formed by union of a branch from each cervical 

 nerve, through the middle, to the inferior cervical ganglion 

 — both of which ganglia are situated between the two first 

 ribs. These structures are hid from view by 



Scalenius, a muscle composed of two distinct heads, the 

 superior or shorter arises from the transverse j^rocess of 

 the seventh cervical vertebra and runs to the anterior 

 margin of the inferior extremity of the su23erior third 

 of the first rib ; the longer or inferior arises from the 

 transverse processes of the fourth, fifth, and sixth 

 cervical vertebrae, and its fibres converge to become in- 

 serted into the superior part of the inferior third of the 

 external surface of the first rib. Between the two heads the 

 axillary ^plexus of nerves ]jasses, heloio the inferior head, the 

 axillary artery and vein, the latter heincj inferiorly sitimted. 

 On removal of this muscle we see the origin of the axil- 

 lary plexus from the sixth, seventh, and eighth cervical, 

 and first dorsal, and sympathetic nerves, and the phrenic, 

 running in a direction backwards, having originated by 

 fibres from the fourth, fifth, and sixth cervical. At the 

 janterior part of the neck longus colli is covered by the 



