opening being more dorsal than the left. The opening has a crescentic lower border,
the concavity of which looks up the (esophagus, and at the opening a portion of
the mucous membrane of each cavity is opposed to that of its fellow. The
common orifice has a capacity, in an individual about 6 feet long, of about 2 inches
in breadth, when moderately distended. The two cavities are united to each other
only immediately below the common opening, and in the individual already mentioned
the attachment is 1*60 inch in one direction and 1*50 in another.
Microscopic characters of the membrane of the first cavity.—A portion of the
adult stomach, in which a layer of the mucous membrane was peeling off, showed
this, under a low power of the microscope, as divided into two parts by a dark line
corresponding to the line of desquamation, although the two were still connected
together. The external there appears much more dense than the internal layer, and
the former is of a uniform consistence, giving no indications of separation into
thinner layers. I t rqust be borne in mind that this desquamation of a surface layer
of this cavity cannot be regarded as a post mortem phenomenon, for in the specimen
in question the stomach was removed as soon as the animal died; even by that time
the limit of effete mucosa had been already indicated at those points where the
tissue had not become separated. The same condition I have observed in more
stomachs than one.
This natural shedding of a superficial layer of the membrane of this first gastric
cavity receives elucidation on a further study of the constituents of the entire wall
of the organ being made. Consult PI. XXXVI, figs. 12 and 13, and compare fig. 14
of a corresponding piece of the same gastric cavity of Orcella, already described. In
that of Platanista under a low magnifying power (Eig.12), the epithelial layers,
desquamative ayl subjacent, are but of moderate thickness, relative to that of the
entire wall of the stomach. The body of the connective and vascular tissue beneath
these is on the contrary very thick,, while the muscular and serous coats are of
medium thickness. Under a much higher power, and thus greatly enlarged (Eig. 13)
the characteristic features are easily resolved. The free internal surface is composed
of a stratified mass of homy epithelial scales (ep) in different stages of development.
Layer after layer of these then must be given off as digestion proceeds, and the
phenomenon of desquamation above mentioned must be, as inferred, a natural
process of constant occurrence.
The second layer in close continuity with the first is analogous to the columnar
cell-layer already described as existing in the first gastric cavity of Orcella (Eig.
14, eg). I t is, indeed, only a continuation downwards of the epithelium, the cells
assuming less of a horizontal, and more of a vertical, position. In J?latanista, moreover,
as contradistinguished to Orcella, the descending columns are far shorter, broader,
fi.nrl club-shaped. In fact, the columno-epitheliai double layers of the former genus
altogether are little more than half the depth of the latter. This coat of the first
stomach in both animals may aptly be compared to the cuticular layer of the skin,
the deeply placed prolongations being nothing more or less than a mucous or Malpighian
layer. They are not, in any sense, true gastric secreting follicles, as in the
ordinary mammalian digestive stomach, for they are solid compact masses of cells
without exterior orifice, apparently do not secrete gastric juice, and only develope
cylindrical epithelial cells, which latter are modified in figure, &c., as they rise to the
surface. In some respects they may be regarded in the light of mucous glands, the
stratum homologically being equivalent to the gastric or peptic glands of the mammalian
stomach generally. I t would thus appear the latter sort are absent in this
first gastric cavity, and instead, mucous glands, such as are found in quantity in the
cardiac area of the stomach of the horse, alone are present. This condition of things
recalls the coats of the gizzard of birds, where in some forms not only is there a
thin partial desquamation of the superficial cells, but the entire homy layer is
periodically shed and renewed.1 .
The submucous or alveolar layer (Eig. 13, c) of this first cavity in Tlatamsta is,
as usual, composed throughout of connective tissue, scattered through which are
spindle-shaped cells, and blood vessels and capillaries in quantity.
The muscular layer (Eig. 13, m), in vertical section, presents fibres cut crosswise
and lengthwise, corresponding therefore to the different direction of the fleshy
bundles, and the fibro-serous layer (fs ) is unusually thick.
Second or right cavity.—(PL XXVI, fig. I, II.)—This is irregularly pyriform,
the stalk of the pear-like figure being the oesophagus, the body being bent to the left
side so that the right is much rounded and more extensive than the left, deeply
concave margin. I t does not reach to so low a level as the first cavity, than which
it is less capacious. Its walls áre not so firm as those of the left cavity, nor so thick,
neither have I ever observed it to become similar to that of the cesophagus, however
great may be the changes which the mucous membrane may undergo, for it is always,
more or less rugose. I t is found generally thrown into very deep folds and is densely
covered with fine mg®, but nearly all the former are permanent, whilst the latter are
transitory. Corresponding to the most concave portion of the left wall of the second
cavity, a permanent fold is found encircling the inside of the sac obliquely from left
to right, and below it there is a short strong crescentic fold stretching from the anterior
on to and along the posterior wall, till on a level with the lower border of the
cavity. The free margin of this almost valvular fold is directed ventrally and to
the right side. A short way behind it, another and shorter fold stretches in the
opposite direction from the posterior on to the anterior wall, and has its free margin
directed dorsally and to the left side. These two folds are occasionally so strongly
marked that they almost divide the apex or fundus of the second cavity into two distinct
chambers, but, as they are not continuous around its walls, the division is very
imperfect. , In other states, although the folds are present, there is no appearance of
division of this cavity into separate chambers.
In an active stomach the whole of the inner surface of the second cavity presents
a uniform structure and character throughout its whole extent. A spirit specimen
has a greyish-brownish tint, and the mucous membrane is thrown into an immense
number of well-defined, finely convoluted rag®. In this cavity, in an old female, the
: Murie : Proc. Zotil-. Soc., 1874. p. 423.