238 
DBS. A. CAETE AND A. MACALISTEE ON THE ' 
tidean folds of mucous membrane, and was distributed to the mucous membrane lining 
the larynx, apparently giving off no muscular branches. 
On raising and reflecting the ala of the thyroid cartilage an accessory aryteno-epi- 
glottideus muscle was exposed ; it was somewhat triangular in shape, and arose from the 
anterior and external angle of the arytenoid cartilage ; from this the fibres passed in- 
wards, diverging, and were inserted into the side of the fibrocartilaginous pedicle of the 
epiglottis, posterior to which its fibres coalesced with those of its fellow of the opposite 
side. 
The thyroarytenoid muscle was united to the posterior border of that last described, 
in fact both appeared to be but parts of one large muscular expansion ; it arose from 
the vertical median ridge onthe superior surface of the thyroid cartilage, where its fibres 
were distinctly separate from the foregoing muscle ; it passed forwards and inwards, and 
was inserted into the anterior and external margins of the arytenoid cartilage, and into 
the contiguous margin of the cricoid. 
There were no vestiges of chordae vocales or of a ventricle, or a lateral laryngeal sac- 
culus ; but situated in front of the cavity of the larynx, and opening by a wide orifice 
immediately at the root of the epiglottis, there was a remarkable large musculo-membra- 
nous mesial sac or laryngeal pouch, which extended downwards and backwards in front 
of the trachea ; its walls, which were thick, were almost entirely composed of circular 
muscular fibres, which anteriorly or nearer the glottis took their origin from the upper 
surface of the thyroid cartilage, and posteriorly formed a series of circles with no defi- 
nite origin or insertion. The interior of this cul-de-sac communicated directly with the 
central portion of the laryngeal cavity by a wide orifice, and was lined by a continuation 
of the mucous membrane of the former. 
-From the situation and structure of this pouch its probable use was to assist, by the 
contraction of its walls, in the act of expiration, increasing the expulsive force of the re- 
spiratory apparatus, by the sudden contraction of its circular fibres expelling the con- 
tained air, and so not only considerably augmenting this power, but also sustaining the 
expiratory current, more especially towards the termination of this act. 
It might also be suggested as an organ for the production or modulation of sound, if 
these animals possessed such a faculty, which must be considered as very doubtful. The 
great size of its laryngeal aperture, and the absence of all constricting bands or apparatus, 
militates considerably against the latter use of this organ. 
A dissection of the soft part of the upper surface of the head exhibited the relative 
anatomy of the 
External nares. 
These were two semilunar slit-like orifices situated on the superior surface of the 
cranium acted on by three separate planes of muscular fibres. The lips of these aper- 
tures, which have already been described, would permit a complete approximation, as 
also of considerable divarication. 
The first or most superficial plane of muscular fibres consisted of the dilator naris, 
