108 
corresponds with the posterior surfaces of the 
arytenoid cartilages, and is connected by some 
muscular fibres and membrane with the supe- 
rior margin of the cricoid cartilage and with 
the whole length of the internal margins of the 
arytenoid cartilages. The immediate effect of 
the contraction of the arytenoid muscles is to 
approximate the posterior internal surfaces of 
the arytenoid cartilages, but their action, at the 
same time, tends to separate the anterior pro- 
minences, and to open the chink of the glottis. 
To counteract this effect the action of the crico- 
arytenoideus lateralis is called simultaneously 
into play, and the joint effect of these two 
muscular forces, represented by the lines N X 
and NY (fig. 30,) produce a resultant in the 
direction of W N ; hence the crico-arytenoideus 
lateralis and the arytenoideus muscle acting 
together tend to close the glottis posteriorly. 
Lhe thyro-arytenvideus.— This is one of 
the most important, most complicated, and 
perhaps least understood of any of the muscles 
of the larynx. It arises from the side of the 
angle of the thyroid cartilage, occupying about 
two-thirds of its height, and reaches within 
two or three lines of its superior margin. The 
central fibres are directed horizontally back- 
wards and outwards, slightly inclined upwards, 
and inserted into the prominence and concavity 
on the lateral surface of the arytenoid(/, fig. 27). 
The superior fibres terminate in the external 
ridge of the arytenoid; some of them pass 
round the arytenoid, and enclose the arytenoid 
muscle like a sphincter.* The inferior fibres 
which arise near the median plane (k, 29) 
are inserted, at a greater distance from it, into 
the arytenoid cartilages (f, fig. 30); some ex- 
ternal fibres are directed more eccentrically 
Fig. 29. 
A view of the larynx from above. ( From Mr. Willis. ) 
The mucous membrane is removed to shew the 
ligaments and muscles of the glottis. NF, NF, 
the arytenoid cartilages; T V, the vocal ligaments ; 
N X, the right crico-arytenoideus lateralis, the left 
is removed ; Xv L, the ring of the cricoid capable 
of rotating on the axis RS; ee, the crico-aryte- 
noidei postici ; E, the junction of the wings of the 
thyroid. 
* Lauth, Mem. de l’Acad. de Méd. 1835. 
NORMAL ANATOMY OF THE LARYNX. 
‘ligaments consist of nothing more than th 
Fig. 30. 
A portion of Sig. 29 ed to demonstrate ti 
ae and result of the forces of the 
OP, the horizontal projection of the ax 
articulation; TV, the vocal ligament; gh, 
direction of the force of the thyro-aryte: 
N X, of the crico-arytenoideus lotrel 
? 
of the crico-arytenoideus posticus; N 
arytenoideus transversus. 
upwards and backward, coreeponeay 
superior ligaments and ventricles, 
cording to Lauth, they terminate 
reaching the arytenoid. Some fibres « 
thyro-arytenoid take an oblique direction 
wards and downwards, arising immed 
below the superior internal margin of the ai 
of the thyroid, and are inserted into the ve 
tical prominence of the arytenoid cartila 
they are sometimes detached from those pass' 
horizontally, as in d, (fig 28,) constituting i 
thyro-arytenoidei —— of Albinus, t 
they are sometimes described as one muscle 
‘he thyro-arytenoideus corresponds to 
internal surface of the thyroid cartilage, fre 
which it is separated by some loose cellu 
and adipose tissue. Internally it is in conte 
with the inferior vocal ligament, which li 
contact with the thickest part of this mu 
the bulk of which causes the vocal ligame! 
on each side to project towards the mesial 
and contracts the aperture of the larynx. Son 
anatomists consider that the thyro-aryt 
tendons of these muscles; it is not diffie 
however, to prove the contrary by dissecti 
The functions of the thyro-arytenoidei, eo 
cerning which there has been much diversity 
opinion, produce several changes in the re 
tive position of the internal mechanism of 
larynx, and therefore they require rigid in 
tigation. The effects of these muscles m 
be considered, first, with respect to the 
of the vocal ligaments; secondly, to the ap 
ture of the glottis. We observe that the poi 
of attachment (at dd’ J, fig. 27) of the th 
tenoid are situated within those 
(fig.28); and, as the arytenoid cartilage is 1 
by ligamentous fibres to the point B, it follo 
that the contraction of this muscle will dra’ 
the point B, through the interposed aryten 
cartilage: if A be made the fixed point, 
contraction of this muscle will draw the poi 
B towards A by rotating the cricoid on the’ 
roid. If, on the contrary, B be fixed, then 
will approach B by the rotation of the thyroi 
on the cricoid. In both these cases the d 
tance from A to B is diminished, and as @ 
vocal ligaments are situated in a direct Iii 
