924 THE RESPIRATORY SYSTEM. 
Relations of the Trachea.—In the study of the relations of the trachea it is 
convenient to consider it in the two stages of cervical and thoracic. 
When the ehin is held so that the face looks forwards the cervical part of the. 
trachea measures from 2 to 25 inches in length; but when the head is thrown 
ithgroianeay back the length tS consider- 
Tete ably increased. Inits upper 7 
j part the trachea is clasped by 
the thyroid body, the isthmus 
SM Conentdecerericienters of which is applied to its 
i) 
iiforominvamidlarters anterior surface, and covers 
Recurrent laryngeal nerve the second, third, and fourth 
~e “Cisophagus rings, whilst on each side 
the lateral lobe of the same 
body is applied to its lateral 
surface, and extends down- 
@_ ene sey wards as low as the fifth ring. 
Zz On either side of the cervical 
ue trachea is theeommon carotid 
eae, artery, whilst the recurrent 
laryngeal nerve ascends in 
ane the groove between the 
trachea and the cesophagus. 
neice non INBLOMSINATIC Aa Posteriorly the trachea is in 
carotid artery” ee relation to the cesophagus, 
: | Rabe ee : j 3 
Pleura \ 2 7 Phrenic nerve which intervenes between 1t 
ees and the bodies of the verte- 
agus ne 
> “ff 
7 — Trachea 
SEES ies \. } 2 eri 
.. subelavian artery 4 bre, and deviates somewhat 
Z laa nerve 
a recurrent So to the left as it descends. 
In addition to the isthmus 
of the thyroid body two thin 
muscular strata, composed of 
the sterno-hyoid and sterno- 
thyroid muscles, and also the 
deep fascia and imtegument, 
separate the cervical trachea 
laryngeal nerve  \ 
Qisophagus 
Pleura 
J, xesentcn from the surface. In the 
YY a middle line of the neck there 
is a narrow diamond-shaped 
D. i Vagus nerve ae. : a 
Siig space between the inner 
Fg torvostel arteries margins of these muscles, 
iS inerely covered by the integu- 
Thoracic duct//  * OY ments and fascie. It is 1m- 
portant to note that in the 
lower part of the neck the 
fz eo azygos major within which the trachea is 
Bifurcation 
__ Sa= of trachea deep cervical fascia is in two 
Vagus = Ss : ae nies Eparterial bronclius layers—viz. a strong stratum 
« Vagus nerve apphed to the anteriorsurtace 
Nee ol Bronchial artery f tl , terme if Ol 1 on 1 
Vena azygos major 0 ey at) ert 0 - Ny Ole ant 
eye: Csophagus sterno-thyroid muscles, and 
Thoracic duct v 4 
a weaker superficial layer 
Fig, 626.—TRANSVERSE SECTIONS through the trachea and its imme- stretching across between the 
Soe at the level of each of the upper five dorsal two sterno-mastoid muscles. 
i Beneath these muscular and 
fascial layers the inferior thyroid veins descend on the surface of the trachea, and 
sometimes the occasional thyroidea ima artery passes upwards in front of the tube. 
At the upper border of the manubrium sterni the innominate artery may be seen 
crossing the trachea obliquely. 
The thoracic part of the trachea is situated in the back part of the superior 
