The section passes through the temporo-mandibular articulation, but is
slightly oblique. _1_, Corpus callosum; _2_, lateral ventricle of
brain; _3_, caudate nucleus; _4_, internal capsule; _5_, lenticular
nucleus; _6_, optic chiasma; _7_, middle cerebral artery; _8_,
sphenoidal sinuses; _9_, cavernous sinus; _10_, Eustachian tube,
inner lamina; _11_, _11_, guttural pouches; _12_, soft palate; _13_,
epiglottis; _14_, hyo-epiglottic muscle; _15_, thyro-hyoid muscle.
]
The principal =relations= of the œsophagus at its origin are: to the
cricoid cartilage below; to the guttural pouches and the ventral
straight muscles above; and to the carotid arteries laterally. In the
middle of the neck the relations are: to the left longus colli muscle
above; to the trachea internally; to the left carotid artery, vagus,
sympathetic, and recurrent nerves externally. At its entrance into the
thorax it has the trachea on its inner side; the first rib, the roots of
the brachial plexus of nerves and the inferior cervical ganglion
externally. After gaining the upper surface of the trachea, it has the
aorta on its left and the vena azygos and right vagus nerve on its right
side. In its course through the posterior mediastinum the œsophageal
trunks of the vagus nerves lie above and below it, and the œsophageal
artery is dorsal to it.
=Structure.=—The wall is composed of four coats: (1) A fibrous sheath;
(2) the muscular coat; (3) a submucous layer; (4) the mucous membrane.
The =muscular coat= is of the striped variety as far as the base of the
heart, where it rapidly changes to the unstriped type. In addition to
this change, the muscular coat becomes much thicker and firmer, while
the lumen is diminished.[86] The outer fibers are arranged
longitudinally, beginning in two bundles attached in the interval
between the arytenoid and cricoid cartilages. The inner fibers run in
two spiral strata to the terminal part of the tube, where the
arrangement is an outer longitudinal and an inner circular layer.[87]
The =mucous membrane= is pale, and is covered with squamous stratified
epithelium. It is loosely attached to the muscular coat by an abundant
submucosa, and lies in longitudinal folds which obliterate the lumen
except during deglutition.
=Blood-supply.=—Carotid, broncho-œsophageal, and gastric arteries.
=Nerve-supply.=—Vagus, glosso-pharyngeal, and sympathetic nerves.