1888 - 89 .] Woodhead and Gray on Stomach of Narwhal. 803 
The interpolation of a single simple communicating tube, devoid of 
gastric function, would be an anomaly ; and they adduce further 
argument, that for the purpose of communication a mere orifice, 
similar to those between the other compartments, would serve 
equally well. 
On these grounds, we are inclined to agree with those who con- 
sider this to be a distinct gastric compartment, in addition to which 
we might adduce the following : — 
The mucous membrane consists of a series of glandular tubes 
lined with distinct secreting epithelium, as already described. 
Although there is no regular valvular fold of mucous membrane 
at either orifice, these orifices will neither of them admit of the 
passage of more than a single finger, and the circular muscu- 
lar fibres around the constricted portions will, in these positions, 
have greater contracting power than around the more dilated 
portions, and they must exert a sphincter action rather than assist 
in producing peristaltic movement, more especially as they lie at 
each end of the dilated portions of the tract. 
The Third True Digestive Cavity. 
This cavity, in certain respects, resembles the human stomach, 
being somewhat cylindrical and crescentic in form, and slightly 
curved upon itself lengthwise, with a well-marked fundus at the 
proximal end. Internally it measures, while moderately distended, 
7 inches in its longest diameter by 3 inches in its shortest. Both 
orifices lie in its lesser curvature, the distance between them being 3 
inches. Of these the first has already been noticed; while the second, 
leading into the fourth true gastric compartment, is slightly larger, 
being fully 1 inch in diameter. The mucous membrane is raised 
into imperfectly marked folds throughout the interior of the cavity ; 
it also forms a slightly elevated ridge at the distal orifice, but there 
is no regular valve present. 
Structure of the Walls . — The fibrous, muscular, and submucous 
' coats are arranged as in the previous compartments, and the gang- 
lion cells, although less numerous, are also present in the areolar 
tissue of the submucous and peritoneal coats. In these situations 
there are also small collections of lymph follicular tissue. 
Mucous Membrane . — In this we find only one kind of glands 
