where they bend backwards is augmented to 0*72 inch. The cricoid cartilage is strong
and compact, with a prominent dorsal ridge, which terminates anteriorly in a
rounded projection, directed forwards and slightly upwards. The surfaces of the
cartilage external to the ridge are concave, and, on looking at them from below, they
are seen to have their margin somewhat everted. The margin anterior to the
attachment of the arytenoid cartilages is concave, and the articulation for those
structures to the cricoid, unlike that of the thyroid, is a capsular synovial joint, which
Turner has also observed to be the case in the great Firmer (Sibbaldius). The
cricoid ring is thick, but there is a great hiatus between it and the posterior border
of- the body of the thyroid, due to the circumstance that the cricoid cartilage simply
roofs in this portion of the cavity of the larynx. The passage through the cricoid
ring is an inch broad, by 075 inch high. The body of the cartilage becomes much
ossified in the adult.
Each arytenoid is a slightly oval laterally compressed cartilage, more pointed
posteriorly than anteriorly, about 1 inch long by 070 inchin breadth. I t presents
three principal surfaces, an anterior, an external, and a posterior. The first is slightly
concave in its centre, and its inner margin expands in its upper half into a triangular
secondary surface, to which a downward process of the anterior horn is attached.
At the upper end of this secondary surface is the narrow isthmus, from which the
anterior horn is projected. The limited nature of the structural union existing
between the body of the arytenoid and its horn, permits the latter to have considerable
mobility. The posterior surface of the body presents the elongated oval
depression for articulation with the cricoid. The internal surface is broad above,
pointed below and' convex, and its posterior margin is continuous above with
the upper border of the cricoid articular surface, anterior to which on the apex of
the cartilage, and immediately behind the base of its anterior horn, is a small
flattened secondary triangular area. The anterior horns are directed upwards and
then forwards, so that their anterior borders are concave to rest against the epiglottidean
cartilage. They are small laterally compressed structures, their inner surfaces
being perfectly flat, so that the two cartilages can be closely opposed to each other.
Their front and posterior margins are sharp, except in the basal half of the latter, which
expands into a flat surface. At the point where the horn springs from the body, and
depending from it, a short process rests against the inner margin of the first secondary
surface of the body. This process or horn is prolonged backwards, as it were, by a
variable number of small cartilages, usually three, closely applied to the inner
margin of the anterior surface of the arytenoid, and are thus included in the
aryteno-epiglottidean membrane. Anterior to the downwardly projecting process
from the base of the anterior horn of the arytenoid, is another narrow rod, arching
outwards and downwards, and occasionally divided at its extremity into two. In its
position and relation this is the equivalent of the posterior horn of the arytenoid.
I t is sometimes, however, only connected to the arytenoid by fibrous tissue. Lying
between it and the cuneiform cartilages already described, occur two or three other
similar yellow cartilages, but varying in number and size. The largest is about 0*25
inch in length by 0T0 in breadth in some instances, but-occasionally they are so small
that they are liable to be overlooked. The epiglottidean when removed from the
thyroid cartilage and its arytenoid surface placed flat, resembles a heel-less boot, the
dorsum being the anterior border of the cartilage, and the sole corresponding
to the concave portion, which latter is applied to the arytenoids. The toe, of course,
is enormously expanded, with two small lateral horns, and is the apex of the cartilage.
The back of the boot, the surface applied to the thyroid, is concave, but filled up
in the recent state with the strong attachment of the thyro-epiglottidean ligament.
The anterior angle of its thyroid surface, when denuded of membrane, is seen to be
formed by a distinct cartilage triangular in form, and measuring nearly an inch in
length and 0‘25 inchin its greatest breadth. I t occupies a position on the epiglottis
in which some such arrangement would be expected, for it occurs opposite to that
part of the cartilage which faces the body of the arytenoids and fills up a gap between
them, the mobility caused by the fibrous attachment of the two aiding the perfect
apposition of the aryteno and epiglottidean mucous surfaces. This supernumerary
cartilage is tipped at its rounded margin by one or two minute but distinct cartilages.
The anterior margin of the cartilage at its extremity divides in two, and forms
a notch through which passes the aryteno-epiglottidean ligament; this passes backwards
to be attached along the dorsal aspect of the body of the thyroid, as far as the
notch. The sides of the cartilage of the epiglottis are covered by numerous pits for
the reception of glands. ■
Trachea.—Before its division this is very short, the bronchus to the apex
of the right lung being given off a couple or three inches from its commencement;
the bronchi to the middle and base of the right lung and to the left lung respectively,
being given off, as it were, by the conjoint bifurcation of the rest of the tube.
On reaching the apex, the first bronchus divides into two principal branches, which
follow the method of division of the trachea, i. e., divide each into three branches.
The second bronchus when it reaches the lung gives off three small branches, one after
the other, to the external portion of the penultimate fourth of the organ, the main
portion being directed to the middle of the lung, and dividing dichotomously. The
third or left bronchus divides into two before it reaches the lung; the left branch
being directed to the apex and the right to the rest of the lung.
The diameter of the trachea is greatest transversely. The cricoid cartilage is
succeeded by a broad flattened ring of cartilage, varying according to the age of the
individual from 0*25 inch to one inchin antero-posterior extent. On its side it is
sometimes cut into by a fibrous band, so that it is quite possible that in some instances
it may be much narrower by a separation of a portion of itself as a separate ring; and
on its dorsal surface it shows a distinct tendency to break up into small plates. I t is
succeeded by a flattened band of cartilage which, commencing by a free end on the
dorsal surface of the right margin of the trachea, passes round to the left, i. e., along
the ventral surface till it reaches the left margin of the tube. There it suddenly
bends on itself and passes behind its first portion, again to the right, along the
ventral surface, so that it does in no way form the dorsal wall of the tube. But two
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