THE TRACHEA 



449 



hyoideus lies on the ventral surface.' The scaleni lie on either side near the en- 

 trance to the thorax. 



The thoracic part of the trachea passes backward between the pleural sacs and 

 divides into the 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-cervieal and vertebral 

 vessels, and the right vagus nerve. Ventrally it is related to the anterior vena 



Obliquus 



capitis |i ■ 

 posterior 

 Intertrans- -i 



versalis 

 Trachelo- 

 mastoideus 

 T 



Rectus capitis — ^v- \ 

 anterior major 

 Mastoido- ~ 



humeralis 



Vagosympa- 

 thetic trunk 

 Carotid artery 



Recurrent nerve 

 Jugular vein 



Omo-hyoideus 



Sterno- 

 cephalicus 



Sterno-thyroideus Sterno-hyoideus 



Fig. 357. — Cross-section of Ventr.\l Part of Neck of Horse. 

 The section is cut at right angles to the long axis of the neclc, passing through the junction of the second 

 and third cervical vertebrae. S.c, Spinal cord; S.v., spinal vein; V.v., V.a., vertebral vein and artery; T.p., 

 transverse process (tip); F, intervertebral fibro-cartilage; T, atlantal tendon common to mastoido-humeralis, 

 splenius, and lower part of trachelo-mastoideus; M, digitation of mastoido-humeralis inserted by T. 



cava, the brachiocephalic and common carotid trunks, and the left recurrent 

 nerve. 



The bifurcation of the trachea (Bifurcatio trachese) is situated opposite to the 

 fifth intercostal space, and about five or six inches (ca. 12 to 15 cm.) below the 

 seventh and eighth thoracic vertebrae. 



The trachea is composed of — (1) A fil)ro-elastic membrane in which are 

 embedded (2) the cartilaginous rings; (3) a muscular layer; (4) the mucous 

 membrane. The elastic membrane is intimately attached to the perichondrium 



1 The arrangement of the niuscle.s should be noted, since the space inclosed bj^ the divergence 

 of the sterno-cephahci and tlie convergence of the omo-hyoidei is the area of election for the 

 operation of tracheotomy. 

 29 



