524 RESPIRATORY SYSTEM OF THE HORSE 
lymph ducts and cervical lymph glands. The cesophagus lies on its left face from 
the third cervical vertebra backward. The sterno-cephalicus muscles cross it very 
obliquely, passing from the ventral surface forward over its sides, and diverging to 
reach the angles of the jaw. The omo-hyoidei also cross it very obliquely, passing 
over the lateral surfaces of the tube, and converging ventrally in the laryngeal 
region. ‘The sterno-thyro-hyoideus lies on the ventral surface.'! The scaleni lie on 
either side near the entrance to the thorax. 
The thoracic part (Pars thoracalis) of the trachea (Figs. 553, 554) passes back- 
Obliquus 
capitis 
posterior 
Intertrans- 
versalis 
Longissimus 
capitis et atlantis 
T 
Rectus capitis 
ventralis major 
Brachiocephalicus 
humeralis 
Vago-sympa- 
thetic trunk 
Carotid artery 
Recurrent nerve 
Jugular vein 
Omo-hyoideus 
Sterno-__ 
cephalicus 
Sterno-thyroideus — Sterno-hyoideus 
Fic. 468.—Cross-secTion oF VENTRAL Part or Neck or Horse. 
This section is cut at right angles to the long axis of the neck, passing through the junction of the second and third 
cervical vertebra. S.c., Spinal cord; S.v., spinal vein; V.v., V.a., vertebral vein and artery; 7p., transverse process 
(tip); F, intervertebral fibro-cartilage; 7’, atlantal tendon common to brachiocephalicus, splenius, and longissimus 
atlantis; M, digitation of brachiocephalicus inserted by T. 
ward between the pleural sacs and divides into two bronchi over the left atrium of the 
heart. It is related dorsally to the longus colli for a short distance, and beyond this to 
the eesophagus. Its left face is crossed by the aortic arch, the left brachial artery, and 
the thoracic duct. Its right face is crossed by the vena azygos, the dorso-cervical 
and vertebral vessels, and the right vagus nerve. Ventrally it is related to the 
anterior vena cava, the brachiocephalic and common carotid trunks, and the car- 
diac and left recurrent nerves. 
1’ The arrangement of the muscles should be noted, since the space enclosed by the divergence 
of the sterno-cephalici and the convergence of the omo-hyoidei is the area of election for the opera- 
tion of tracheotomy. 
