52-i 



RESPIRATORY SYSTEM OF THE HORSE 



lymph ducts and cervical lymph glands. The oesophagus 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- 



Ohliquus 

 capitis 

 poslurior 

 Inter trans 

 versalis 

 Longissimub 

 capitis et atlantis 

 T 



Rectus c 

 ventralis i 

 Brachiocephal 

 hum. 



Vago-. ji 



thcti t 



Carotid a 



Recurrent nerve 

 Jugular rein 



Sterno- 

 cephalicus 



Omo-hyoideus 



Sterno-thyroideus Sterno-hyoideus 



Fig. 468, — Cross-section of Ventral Part of Neck of 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 vertebrge. .S.c, Spinal cord; S.v., spinal vein; V.v., V.a., vertebral vein and artery; T.p., transverse process 

 (tip) ; F, inter^^ertebral fibro-cartilage ; T, atlantal tendon common to brachiocephahcus, 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 oesophagus. 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 stemo-cephalici and the convergence of the omo-hyoidei is the area of election for the opera^ 

 tion of tracheotomy. 



