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Rosenberg, E., Ueber Umformungen an den Incisiven der zwciten Zahngeneration des Menschen,
Morph. Jahrb. xxii, 1895.

Ryder, J. A., On the mechanical genesis of tooth forms, Proc. of the acad. of sci. of Philadelphia,
1878 and 1879.

Sag-emehl, M., Die Ueberzald und Unterzahl in den Zahlen des menschliche Gebisses mit
Einschluss der sogenannten Dentitio tertia, Deutsche Monatsschrift fur Zahnheilkunde, Dec. 1886.

Scnaffer, Josef, Ueber Roux'sche Kandle in menschlichen Zahnen, Sitzungsb. der kais. Akad. der
Wisaensch. Abt. iii, Bd. xcix, 1890.

Scheff, J. , Retention, Rudimentdrzahne, u. s. to., Handb. der Zahnheilk., Bd. i, 1891.
Scheff, J., Junr., Ein Fall von drei beiderseits im Unterkiefer typisch ausgebildeten Backzahnen,
Oesterr. -ungar. Vierteljahrsschr. f. Zahnheilk., 1890.

Schiff, J., Ueb. das Rudimentdrwerden des IVeisheitzahnes (Dens Sapientice), Wien. med. Presse,
1887.

Schlosser, M., Ueber d. Deutung d. Milchgebisses d. Sdugethiere, Biol. Centralbl. x, 1890, and
Verhandl. d. deutsch. odont. gesellsch., Bd. iv, 1893.

Schmid, H., Zur Casuistik der Zahnanomalien, Prager Zeitschr. f. Heilkunde, 1886.
Schmidt, L., Ueber die Bedcutung des ersten Mahlzahnes, Deutsche Monatsschrift fur Zahn-
heilkunde, 1887.

Schmidt, W., Ueb. Grossenverhdltnisse der Zahne, Zahntechnische Reform, xii, 1892.



56 OKGAXS OF DIGESTION.

Schwalbe, GK, Ueber Zahnentwickeluny und Zahmvechsel, (Naturwiss. med. Ver. in Strassbnrg
i. E.), Wiener klinische Wochenschrift, 1893 ; Ueber eine seltene Anomalie des Milchgebisses beim
Menschen und ihre Bedeutung fur die Lehre von den Dentitionen, Morphol. Arb., Bd. iii, 1894 ;
Ueber Thcorien der Dentition, Verhdlg. d. anatom. Gesellsch., 1894.

Scott, W. B., The evolution of the premolar teeth in mammals, Proc. of the acad. of sci. of
Philadelphia, J892.

Smith, A. Hopewell, Some observations on the cellular elements of the dental pulp, Trans.
Odont. Soc., Nov. 1893.

Smith, "Wilberforce, The teeth often Sioux Indians, Journ. Anthrop. Institute, xxiv, 1894.

Sommer, Carl, Zur Histoloyie des Zahnschmelzes, Jahrb. f. Zahnheilk., Bd. vii.

v. Spee, F., Ueber die ersten Voryanye der Ablayerung des Zahnschmclzcs, Anatom. Anz., Jahrg. ii,
1887.

Struiken, H.. Die Rtsorption der Milchzahne und die Odontoklastcn, Centralb. f. d. medicin.
Wissenschaften, 1890.

Sudduth, W. X., Dental Embryol. and Histol. in "American System of Dentistry," 1887.

Symington, J., On the position and relations of the teeth in children, Journal of the British
Dental Association, 1887.

Thomas, Oldfielcl. On the homologies and succession of the teeth in the Dasyuridcc, with an
attempt to trace the history of the evolution of mammalian teeth in general, Philosoph. Trans, of the
Roy. SDC., 1887 ; Notes on W. KiikenthaVs discoveries on mammalian dentition, The Annals and
Magazine of Natural History, 1892.

Tomes, C. S., On the structure and development of vascular dentine, Phil. Trans., vol. clxix,
1878 ; A Manual of Dental Anatom.y , 4th edition, 1894.

Topinard, P., De Involution des molaircs et premolaires chez les primates et en particulier chez
Vhomme, L'Anthropologie, 1892.

Troitzky, De la deuxieme dentition ou de I' apparition des premieres grosses molaircs dans son
rapport avec ia troisieme dentition, c'est-d-dire avec le remplacement des dents du lait par les dents
permantntes ; etat de la deuxieme dentition durant la troisieme, Paris, 1890.

Turner, W., The relation of the alveolar form of cleft palate to the incisor teeth and the inter-
maxillary bone, Journ. Anat. , xix, 1885 ; The relations of the dentary arcades in the crania cf
Australasian aborigines, Journal of Anatomy and Physiology, vol. xxv, 1891 ; A pair of super-
numerary teeth in the molar region, Journ. of Anat. and Physiol., vol. xxvi, 1891.

Virchow, B.., Retention, Heterotypie und Ueberzahl von Zdhnen, Verhandl. d. Berliner
anthropol. Gesellschaft, 1886.

Weil, Li. A. , Zur Histologie der Zahnpulpa, Deutsche Monatsschrift flir Zalmheilkunde, Jahrg. v,
1887; Doppclseitige ZwiUinysbildung der mittleren oberen Schneidezdhne, Anat. Anz., viii, 1893, and
Deutsche Monatsschr. f. Zahnheilkunde, xi.

Wells, A. Li., Osseous union of two teeth, Journ. Brit. Dental Assoc., 1892.

Werner, Ueb. die Zapfcnzdhne des Menschen, Inaug. Diss., Miinchen, 1892.

Wilson, A., The Prcmolars in Man, Journal of British Dental Association, 1887.

Windle, B. C. A., and Humphreys, J., Extra Cusps on the Human Teeth, Anatom. Anzeiger,
Jahrg. ii, 1887 ; Man's Lost Incisors, Journal of Anatomy, vol. xxi, 1886.

Wood-ward, M. J., On the milk dentition of Procavia (Hyrax) capensis, <fcc., and of the rabbit,
with remarks on the relation of the milk and permanent dentitions of the mammalia, Proc. Zool. Soc.,
1892 ; On the development of the teeth of the Macropodidai, Ibid., 1893 ; On the milk dentition of the
Rodentia, &c., Anat. Anzeiger, 1894; On the succession and genesis of mammalian teeth, Science
Progress, Bd. i, 1894.

Wortman, Jacob L., The comparative anatomy of the teeth of the Vertebrata, American
System of Dentistry, vol. i, 1886.

Zsigmondy, Otto, Ueber die Verdnderungen des Zahnbogens bei der ztceiten Dentition, Archiv
f. Anat. u. Physiol., Anatom. Abt., 1890..

Zuckerkandl, E., Ueb. Zahnrctention, und Ueb. rudimentdre Zdhne, Wiener med. Jahrbiicher
1885 ; Ueber das epitheliale Rudiment tines vierten Mahlzahnes beim Menschen, Sitzungsb. der k.
Akad. der Wissensch. in Wien, 1891 ; Anatomic der Mundhohle mit besonderer Bcriicksichtiyuny
der Zdhne, Wien, 1891.



THE PHARYKX. 57



THE PHARYNX.

The pharynx (figs. 76, 77, 78 and 80) extends from the base of tile sTmll to the
lower border of the sixth cervical vertebra, where it terminates by becoming con-
tinuous with the oesophagus. It lies in front of the lower part of the basilar process
of the occipital bone and the upper six cervical vertebrae and behind the nasal
cavities, mouth, and larynx. It may therefore be divided into three parts, viz.,
nasal, oral, and laryngeal. The soft palate projects backwards and downwards into
it, and during the act of deglutition is drawn upwards and backwards against its
posterior wall, so as to completely separate the nasal from the oral portion. In all,
seven openings lead into the cavity of the pharynx, viz., above the velum, the two
posterior nares (choancv} and the two Eustachian tubes, and below the velum, from
above downwards, the orifices leading into the mouth, larynx, and oesophagus.
The pharynx is about five inches (14 centimeters) in length. Its transverse
diameter is considerably greater than its antero-posterior. Its widest part is
opposite the laryngeal aperture, beiow which it rapidly contracts like a funnel
towards its termination, where it is narrowest.

The nasal part of the pharynx (naso-pharynx or post-nasal space) is an air
cavity irregularly cubical in shape, which cannot be obliterated by muscular action,
although its floor can be raised and depressed by the muscles of the soft palate. Its
anterior wall shows the posterior edge of the nasal septum with the posterior nares,
one on either side. In the posterior wall the mucous membrane is thickened and
thrown into a number of folds, chiefly vertical in direction. As these folds contain
a considerable quantity of lymphoid tissue they are often called the pharyngeal tonsil.
A well-marked recess of the mucous membrane, known as the pharyngeal bursa
(recessus pharynyeus medius), which is constant in the foetus and young subject, and
is occasionally present in the adult, extends from just below the pharyngeal tonsil
upwards in the middle line as far as the pharyngeal tubercle.

This recess was regarded by Lusehka (Der Schlundkopf d. Menschen, 1868. p. 26) as a
rudiment of the imagination from which is developed the anterior part of the pituitary body.
This idea is now . generally abandoned in favour of the view that it is connected with the
formation of the pharyngeal tonsil. Killian (Morph. Jahrb., Bd. xiv, 1888, p. 618), however,
has shown that the pharyngeal tonsil may exist in the human foetus and also in animals
without any traces of a pharyngeal biirsa.

The opening of the Eustachian , tube appears as a vertical cleft, or as a funnel-
shaped opening, in the lateral wall, and is bounded behind by a prominence the
cushion of the Euslachian orifice containing the cartilage of the tube. Between
this prominence and the posterior wall of the pharynx there is a deep recess passing
backwards and outwards. It is known as the lateral recess of the pharynx (fossa of
Rosenmuller}. This recess represents the upper part of the pharyngeal portion of the
second visceral cleft, the Eustachian tube being formed from the first cleft. From
the cushion of the Eustachian orifice the mucous membrane forms a vertical fold,
the plica salpingo-pharyngea, passing downwards on the side wall of the pharynx
behind the posterior palatine arch.

When the levatores palati are contracted, the upper surface of the soft palate
presents a convex eminence behind each posterior naris, called the levator cushion,
This is occasionally seen in the dead body.

The average capacity of the nasal part of the pharynx is said to be 14 cubic
centimeters. Its transverse diameter in front of the Eustachian orifices is about
22 mm. ; between the Eustachian cushions it varies considerably on an average it
is about 15 mm. The distance from the lower part of the posterior edge of the
nasal septum to the posterior wall of the pharynx is 15 mm.




Fig. 76. MEDIAN SECTION OF THE HEAD AND NKCK. (Braune.)

1, sphenoidal sinus ; 2, lateral recess of pharynx ; 3, pharyngeal orifice cf Eustachian tube ; 4,
anterior arch of atlas ; 5, soft palate ; 6, body of axis ; 7, oral portion of pharynx ; 8, epiglottis ; 9,
arytenoid muscle ; 10, cricoid cartilage ; 11, trachea ; 12, oesophagus ; 13, origin of innominate artery
from aorta ; 14, genio-glossus muscle ; 15, genio-hyoid muscle ; 16, mylo-hyoid muscle ; 17, platysma ;
1H, hyoid bone ; 19, thyroid cartilage ; '20, cricoid cartilage ; 21, isthmus of thyroid body ; 22, sterno-
hyoid; 23, sterno-thyroid ; 24, left innominate vein ; 25, manubrium sterni.



THE PHARYNX.



59



The oral part of the pharynx is situated below the soft palate and above
the level of the Jarynx. Owing to the mobility of its walls it is very variable in form
and size. In front it communicates with the mouth through the isthmus of the
fauces, and below this opening it is bounded anteriorly by the posterior part of the




- 11



1-2



Fig. 77. HORIZONTAL SECTION THROUGH NASAL CAVITIES AND NASAL PORTION OF PHARYNX, SEEN

FUOM ABOVE. (J. S.) |

1, anterior naris ; 2, septal cartilage ; 3, vomer ; 4, inferior concha ; 5, inferior raeatus ; 6,
maxillary antrum ; 7, posterior naris ; 8, Eustachian tube ; 9, tensor palati ; 10, levator palati ;
11, internal carotid artery ; 1'2, lateral recess of pharynx ; 13, rectus anticus major ; 14, pharyngeal
tonsil.

dorsum of the tongue. On its lateral wall there is a somewhat triangular recess
bounded by two folds of mucous membrane, called the anterior and posterior
palatine arches. Both these folds are connected above with the soft palate, and
diverge as they pass downwards. The anterior arch joins the tongue and forms the
lateral boundary of the isthmus of the fauces, while the posterior one gradually
disappears on the side wall of the pharynx.

The tonsils (tons-ilia, amygdalce,} are two prominent bodies situated in the recess
between the anterior and posterior palatine arches. They are usually from 20 to
2f> mm. in vertical extent, reaching from the soft palate above to the level of the top
of the epiglottis below ; they measure about 15 mm. from before backwards and
rather less than this from within outwards, but they vary much in different indi-
viduals. The free inner surface of the tonsil has a variable number of slit-like or



ORGANS OF DIGESTION.

rounded orifices which lead into recesses or crypts in the substance of the tonsil
(fig. 78, 16 ; fig. 79). The outer surface is connected with the inifer aspect of the
superior constrictor of the pharynx, external to which is the internal pterygoid muscle.
Both the external and internal carotid arteries lie fully an inch external and posterior
to the tonsil. The tonsils extend downwards as low as the angle of the jaw, but they
cannot, even when enlai'ged, be felt from the surface of the neck at this point.

Above the tonsil there is frequently a recess directed upwards and backwards,
and called the fossa supra-tonsillaris. It is considered by His to be the remains of
the lower part of the second visceral cleft. The fold of mucous membrane covering
this recess is named plica triangular is.

Vessels and nerves. Arteries. These structures receive a very large supply
of blood from various arteries, viz., from the tonsillar and palatine branches of the




Fig. 78. HORIZONTAL SECTION THROUGH THE MOUTH, PHARYNX, &c., JUST ABOVE THE TEETH OP

THE LOWER JAW. THE SECTION IS VIEWED FROM ABOVE. (J. S. ) f

1, Body of axis ; 2, ranuis of lower jaw ; 3, orbicularis oris ; 4, buccinator ; 5, masseter ;
6, internal pterygoid ; 7, stylo-glossns ; 8,. stylo-pharyngeus ; 9, digastric and stylo-hyoid ; 10, rectus
capitis anticus major ; 11, longus colli ; 12, sublingual gland, and on its inner side Wharton's duct ;
13, aperture of Wharton's duct ; 14, muscular substance of tongue ; 15, tip of uvula ; 16, tonsil
(somewhat enlarged) ; 17, root of tongue ; 18, epiglottis ; 19, posterior palatine arch ; 20, anterior
palatine arch ; 21, parotid gland ; 22, external carotid artery ; 23, internal jugular vein ; 24, hypo-
glossal nerve ; 25, vagus ; 26, internal carotid artery ; 27, pharyngeal veins ; 28, lymphatic gland.

facial artery, the descending palatine of the internal maxillary, the ascending
pharyngeal and the dorsal artery of the tongue. From these arteries fine branches
and capillaries are distributed abundantly to the lymphoid tissue and follicles and
to the papillae of the mucous membrane which lines the recesses. The veins are
numerous, and enter the tonsillar plexus on its outer side. The nerves come from
the glosso-pharyngeal nerve, and from the fifth. Lymphatics are abundant, and
surround the follicles with a close plexus ; they eventually pass into the superior
deep cervical lymphatic glands.

Structure. The tonsils are composed of a spongy connective tissue infiltrated
with lymphoid cells, which are collected at frequent intervals into nodules or
follicles, in which the lymphoid tissue is denser than elsewhere. These nodules, as
in other situations where they occur, represent germinating centres in which the



THE TONSILS.



61



lymphoid cells are most rapidly multiplying. Extending inwards from the surface
are tubular or cleft-like crypts, which are lined with stratified epithelium similar to
that of the surface, and the walls of w r hich are beset with lymphoid nodules. Into
these crypts mucous glands open, but these are not very numerous. The lymphoid
cells are constantly passing in large numbers through the epithelium, to become free
at the surface and on the crypts of the tonsils (Stohr) ; in this way they pass into
the mouth and mix with the saliva to form the so-called salivary corpuscles.

The laryngeal part of the pharynx is situated behind the entire extent
of the larynx. Its length is equal to that of the nasal and oral parts combined. In
the upper part of its anterior wall is the superior aperture of the larynx. On either




Fig. 79. SECTION THROUGH ONE OF THE UKYPTS OP THE TONSIL, MAGNIFIED. (Stohr.)
e, stratified epithelium of general surface, continued into crypt ; /, /, follicles or nodules of
lymphoid tissue ; opposite each nodule or germ-centre numbers of lymph-cells are passing into and
through the epithelium ; s, s, masses of cells which have thus escaped from the tonsil to mix with the
saliva as salivary corpuscles.

side of this is a longitudinal groove called the sinus pyriformis, which represents the
remains of the fourth visceral cleft (His).

Opposite the laryngeal aperture the transverse diameter of the pharynx is about
3'6 c.m. Below this opening the anterior and posterior walls of the pharynx are in
contact, but the transverse diameter undergoes only a very slight diminution as far
down as the cricoid cartilage, behind which it rapidly contracts so that at its
termination it is only about 12 to 16 mm.

Varieties. The principal variations of the pharynx are due to the abnormal persistence
of the visceral clefts or irregularities in their position. Various cases of this kind have been
described as pharyngeal diverticula or cervical fistulse (for literature, see von Kostanecki).

Structure and attachments. The walls of the pharynx are formed from
within outwards of a mucous membrane, a layer of fibrous tissue called the pharyn-
geal aponeurosis, a muscular coat, and another layer of fibrous tissue, which with
that covering the buccinator muscle, is called lucco-pharynyeal fascia (see Vol. II,



ORGANS OF DIGESTION.



p. 307). The pharyngeal aponeurosis is thin and lax below, but becomes thicker
and denser above, where it is attached to the posterior part of the sphenoid bone
and passes outwards to the petrous portion of the temporal bone and on to the
Eustachian tube. It is strengthened in the middle line by a strong band descending

Fig. 80. HORIZONTAL SECTION OF THE LARYNX AND

LARYNGEAL PART OF PHARYNX. (J. S. )

], thyroid cartilage; 2, thyro-arytenoid muscle; 3,
lateral crico-arytenoid muscle ; 4, arytenoid cartilage ; 5,
rima glottidis ; 6, arytenoid muscle ; 7, cavity of laryngeal
part of pharynx ; 8, inferior constrictor of pharynx.



,-2



.3




between the recti antici muscles from a part of
the basilar process of the occipital bone, which
often presents a marked tubercle.

Behind, the bucco-pharyngeal fascia is con-
nected by a very loose areolar tissue to the
prevertebral fascia, covering the bodies of the

cervical vertebra and the muscles which rest upon them. At the sides it has similar
connections with the styloid process and its muscles, and with the sheaths of the
large vessels and nerves of the neck.

The attachments and relations of its muscular coat are described in Vol. II,
Part ii. Its mucous membrane is continuous at the several apertures with those of
the adjacent cavities.

Structure of the mucous membrane of the pharynx. The mucous
membrane of the pharynx is formed by connective tissue, provided with low
papillae and covered by epithelium, which is stratified over the greater part of the
cavity, but becomes ciliated in the upper or naso-pharynx as far as the level of the
lower border of the soft palate. The back of the soft palate also has a covering of
ciliated epithelium, and a similar epithelium has also been noticed in some of the
gland ducts of other parts of the pharynx. Numerous racemose mucous glands
occur under the mucous membrane ; they are especially abundant above, near the
Eustachian tube, but they are found in all parts. Lymphoid tissue is also abundant
in the upper part and back of the pharynx ; a large collection of lymph-follicles
stretches across the back of the cavity between the orifices of the Eustachian tubes
(pharyngeal tonsil). This is apt to become hypertrophied in children, and to block
those orifices, and even the posterior nares.



RECENT LITERATURE OP THE PHARYNX AND TONSILS.

Albrecht, P., Ueber die morph. Bedeutung der Pharynxdivertikel, Centralblatt f. Chirurgie,
1885.

Anderson, The morphology of the tongue and pharynx, Journ. of Anat. and Physiol., vol. xv, 1881.

Bickel, Ue. d. Ausdehnung 11. d. Zusammenhang d. lymph. (jewebes in der Rachengegcnd Arch
f. path, anat., 1884.

Bowles, R. L., Observations upon the mammalian pharynx, ivith especial reference to the
epiglottis, Journ. of Anat. and Physiol., vol. xxiii, 1889.

Brosike, Ueber einen Fall von Divertikel der Seitenwand des Pharynx in Communication mit der
Tuba Eustachii, Arch. f. path. Anat., Bd. xcviii.

Donelan, J., Supernumerary Tonsils, Brit. Med. Journ., 1890.

Drews, R., Z diver mehruny i. d. Tonsilla palatina, Arch. f. rnikr. Anat., Bd. xxiv, 1884.

Fischer, M. , Ueber die angeborcnen Formfehler des Jiachcns, Inaug. Diss., Wiirzburg, 1892.

Gulland, G-. Li., The development of adenoid tissue ivith special reference to the tonsils and
thymux, Reports of Lab. Roy. Coll. Phys , Edin., vol. iii, 1891.

His, W., A natomie menschl. Embryonen, Leipzig, ]8S5.

Kastschenko, Das Schicksal der embri/onalen Schundspalten bei Saugcthicren, Arch. f. mikr.
Annt., Bd. xxx, 1888.

Killiaii, Ueber die Bursa und Tonsilla pharynyea, Morph. Jahrb., 1888.



RECENT LITERATURE OF THE PHARYNX AND TONSILS. 63

Kircher, Ueber Divcrtikelbildung in der Tuba Eustachii des Menschen, Leipzig, 1887.

von Kostanecki, Kasimir. Zur Kenntniss des Pharynxdiverticulum des Menschen mit
besonderer Berilcksichtigung der Divertikelbildungen im Nasenrachcnraum, Arch. f. path^Anat., Bd.
CKvii.

Mancloire, Depressions ct divcrticules pharyngts, Bull. Soc. anat. , Paris, 1892.

Piersol, G. A., Ueber die Entioickelumg der embry. Schlandspalten und ihrer Derivats bei
Sdugethieren, Zeitsch. f. wissensch. Zoologie, Bd. Ivii.

Poelchen, B., Zar Anatoinie des Nasenrachenraum.es, Archiv f. path. Anat., Bd. cxix, 1890.

Potiquet, La bourse pharyngienne de Luschka, Res. de laryngologie, x, 1889.

Retterer, E., Origine et evolution des amygdales chez les mammif&res, Journ. de I'anatomie,
Annee xxiii, 1888 ; Du tissu angiothelial des amygdales et les plaques de Peyer, Memoires de la
societe de biologic, 1892.

Rieffel, H., Sur les rapports des amygdales avec les vaisssaux carotidiens, Paris, 1893.

Kuckert, J., Der Pharynx als Sprach und Schluckapparat, Miinchen, 1882.

Schwabach, Ueber die Bursa pharyngea, Arch. f. mikr. Anat., Bd. xxix, 1887.

Stdhr, Ph., Ueber Mandeln u. Balydruusen, Arch. f. path. Auat. Bd. xcvii, 1884.

Stuart, Anderson, and M'Cormick, Alexander, The position of the Epiglottis in swallowing,
Journ. of Anat. and Physiol., vol. xxvi, 1892.

Suchaiinek. H. Beitrdge zur norm. u. path. Anat. des Rachengewdlbes, Ziegler u. Nauwerok,
Beitriige zur path. Anat., iii, 1888 ; Anatomische Beilrdge zur Frage iiber die sag. Bursa pharyngea,
Zeitsch. f. Ohrenheilk., xix, 188889.

Symington, J., On nares and epiglottis, Proc. of the Anat. Society, Journ. of Auat. and Physiol.,
vol. xxiii, 1889.

Tornwaldt, Ueber die Bedeutung der Bursa pharyngea, u.s.iv., Wiesbaden, 1885.

"Waldeyer, Beitrdge zur norm. u. vergl. Anatomic des Pharynx mit besonderer Beziehung auf
den Schlingiveg, Sitz. d. k. pr. Akad. der Wissensch. zu Berlin, 1886.

Wheeler, P/iarynyocete and dilatation of the pharynx, Dubl. Journ. Med. Science, 1886.

Zaufal, Die Plica salp ing o -pharyngea, Arch. f. Ohrenheilkunde, Bd. xv.

Zawarykin, Th., Ueber das Epithel. der Tonsillen, Anatom. Anz., Jahrg. iv, 1839.

Zuckerkandl. O., Zur Frage der Blutung nach Tonsillotomie, Wiener med. Jahrb. , 1887.



OEGANS OF DIGESTION.



THE (ESOPHAGUS.

The oesophagus or gullet is the part of the alimentary canal leading from the
pharynx to the stomach. Ifc commences at the level of the lower border of the
cricoid cartilage, opposite the disc between the sixth and seventh cervical vertebra,
and passes downwards through the lower part of the neck into the thorax. In this
cavity it lies in the superior and posterior mediastina, and after piercing the
diaphragm, it ends opposite the tenth or eleventh dorsal vertebra by opening into
the stomach.

The length of the oasophagus is about nine or ten inches (26 centim.). It is of
smaller diameter than any other division of the alimentary canal, its narrowest part
being at the commencement behind the cricoid cartilage ; it is also slightly constricted
in passing through the diaphragm, but, below that, widens into the stomach. It is
usually flattened from before backwards, so that its lumen appears as a transverse
slit (fig. 81), but occasionally it is rounded with the cavity stellate in form (fig. 82).








Fig. 81. HORIZONTAL SECTION OF TRACHEA, (ESOPHAGUS, AND THYROID BODY. (J. S.)

1, oesophagus ; '2, cavity of trachea ; 3, cartilaginous ring of trachea ; 4, thyroid body ; 5, inferior
thyroid artery ; 6, recurrent laryngeal nerve.

Fig. 82. HORIZONTAL SECTION OF THE (ESOPHAGUS AND THORACIC AORTA AT THE LEVEL OP THE

9TH DORSAL VEE.TEBRA. (J. S.)

1, oesophagus ; 2, thoracic aorta ; 3, thoracic duct ; 4, vena azygos major receiving a tributary from
the left side ; 5, body of vertebra ; 6, pleura ; 7, diaphragm.

When empty its greatest diameter is about 20 mm., and when moderately distended,
so that it acquires a cylindrical form, its diameter varies from 18 to 24 mm. It is



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