hyal by tortuous openings through valvular passages. This .compound sac extends
to the middle line, its first portion running along the inner surface of the stylohyal
to its extremity, where its inner wall lies against the upper surface of the caratohyai.
Thus, the .sacs of opposite sides are here only separated from each other by a thin
layer of connective tissue,—so thin, indeed, and the sacs presenting so many crypts
that might communicate with their fellows of the opposite sac, that I had at first
expected to have met with the anomaly of the Eustachian tubes communicating
with each other at the base of the tongue. The second portion of the compound
sac lies between the thyrohyal and the lower portion of the thyroid cartilage, and
extends in front of the latter, and the sacs of opposite sides are here also only separated
by a. narrow interval of connective tissue. In the most anterior portion of the sac,
that lying between the caratohyai and stylohyals, I have found small bones, and,
strange to say, many crystalline lenses of fishes of apparently one size and probably of
one species ; and from one individual I removed two parasitic worms, Ascaris simplex,
which is so prevalent in the stomach and intestines. The whole of this remarkable
sac has its walls covered with valvular folds defining crypts and passages, and, at
the commencement of the portion lying between the thyrohyal and thyroid cartilage,
valvular folds are connected to each other by fine fibrous cords (Pl. XXVIII,
figs. 2 and 5).
The orifices in the posterior nares lie anterior to the epiglottis when in its
normal position, and the downward direction of the external passage is to guard
against the possibility of water finding access by them to the Eustachian system, and
thé valves subserve the same purpose. Still, nature, in avoiding one danger, has in-»
curred another in the apparent tendency which the sacs have to become receptacles
for foreign objects drawn up from the throat in the act of expiration, and which by
their presence might prove the cause of Inflammation and abscesses in the ramifications
of the Eustachian system and at the root of the'tongue. These foreign objects
may doubtless find their way first into the posterior nares by the action of the muscles
which grasp the epiglottis.
Microscopic structv/re of the walls o f Eustachian sacs.—The very remarkable
pouched character of the walls of the foregoing passage and their glutinous surface
led me to investigate their minute structure {vide Pl. XXXVII, figs. 7 and 8),
I find them to be throughout composed of loose folds of thick mucous membrane.
{Short irregular papillæ invest the surface, and everywhere, at scattered intervals, are
small pits and the minute orifices of mucous glands. These glands are most of them
superficially situated, but some are sunk deeper into the tissue, chiefly simple and
tubular. Certain of them nevertheless are slightly racemose ; and all contain cylin->
drical epithelium with often a central cavity. The elevated papillæ already men»
tioned are exceedingly vascular, indeed possess a thick network of fine capillaries,
the parent vessels of which are both numerous and of considerable calibre. This
tube, therefore, must at times be very turgid. The free surfaces of the papillæ are
themselves quite shaggy under the microscope, being covered by a close-set layer of
cylindrical fringed or ciliated epithelium. The deep connective tissue of the submucous
membrane is loose, strong-fibred, but very open, some fat cells and oily
particles being mingled with the tissue, while elliptical-shaped great bundles of the
striped muscular fibres course in different directions, right up almost to the glandular
layer in some instances.
Parotid Gland.—! introduce in this place a short notice of a glandular
structure met with in the neighbourhood of the jaw articulation. I t has no immediate
connection with the Eustachian apparatus, and only claims attention here from
its proximity.
Lying immediately behind the attachment of the stylohyal, and 2-50 inches
behind the articulation of the lower jaw, and on the same level, is a somewhat
crescentic-shaped gland, 2 inches long and 0-75 of an inch broad, in the dolphin 51
inches long. This gland is doubtless the parotid, but I have been unable to detect any
duct; my failure to do so is probably attributable to the condition of the specimen.
Larynx.—(PI. XXVIII, figs. 6 and 7).—The opening to the larynx is a transverse
slit, 1*25 inch in breadth when closed, and a longitudinally oblong orifice when open,
1*25 inch in length and a little more than 0*75 inch in breadth. The tube of the larynx
projects forwards and upwards, generally towards the right side, and is 1*25 inch in
length. There is nothing remarkable in its form, which coincides with that of other
Cetaceans. The 'mucous membrane lining the base of the epiglottis and the
inferior cornua and body of the arytenoids is covered sparsely, in the first locality,
with small papillary processes, which are numerous over the two latter areas. A
short fold of mucous membrane stretches backwards to opposite the posterior border
of the body of the thyroid cartilage, having begun near the middle of the epiglottidean
eartilage and opposite to the tip of the posterior horns of the arytenoids. On each
side of the fold, there is a small orifice which I have been able to trace only a very
short way, and it appears to be a blind sac, and I cannot detect any trace of a
laryngeal pouch. A number of small closed cavities exist in some specimens, but
not in others, and are situated over the body of the thyroid and before the ring of
the cricoid and are most deceptive, for they simulate natural cavities to a wonderful
degree, but the examination of the larynx in four individuals has satisfied me that
they are purely adventitious.
The thyroid cartilage is remarkable for its great lateral expansion. I t con-»
sists of a body with two wings or lateral bars of cartilage projecting outwards and
backwards. The body is lingulate, and projects forwards anterior to the lateral bars,
while its posterior border is notched. Erom the hinder third of the lateral margin
of the body, the bars of cartilage project outwards for 1*50 inch, nearly at right angles
to the body,-with a slightly backward inclination, and each wing projects outwards
and dorsally to protect the anterior two-thirds of the cricoid. I t then bends backwards
and inwards to reach the cricoid. I t presents no trace of an anterior horn.
The thickness of the posterior portion of the cartilage does not exceed 0*10 inch, but
it increases as it approaches the cricoid to more than double that thickness, and the
anterior portion of the body is convex superiorly, and thicker than its posterior half,
or than the lateral bars. The breadth of the latter structures is about 0*40 inch, but