OF THE STURGEON. 
361 
opening, is, in the small specimen, about the size of a six- 
pence, in the large one about the size of a shilling, elliptical, 
rather than round, with the large diameter longitudinally. 
This space presents in this animal four openings. The first, 
which is the largest, is anterior and superior, in the middle, 
and is the termination of the intestinal tube, or the lower 
opening of the spiral intestine. This constitutes the anus 
proper, and is represented at a (Fig. 5.) Behind, and a 
little below this, is another opening, much smaller, but 
large enough to admit a blowpipe or a small quill, and 
forming, by the elevation of its edges, a nipple-like projec- 
tion {n). This, after passing about half an inch inward, 
divides into two canals, large and capacious, on each side of 
the spiral intestine, but behind the peritoneum, and con- 
sequently without that membrane. These canals extend 
upward, widening, and becoming capacious, and present at 
intervals blind cavities, the surface of which is vascular and 
villous. These cavities, which resemble closely in structure 
and appearance the small follicular sacs of the mucous 
membranes in the mammalia, are analogous to the mtfun-' 
dibula of the kidneys in this class ; and the whole canals 
may be regarded as kidneys, arranged in the longitudinal 
form, and terminating in a common urethra^ immediately 
behind the anal orifice, as already stated. The small nip- 
ple-like orifice, therefore, may be regarded as a urethra, or 
at least a common ureter ; and there is, consequently, in 
the sturgeon no cloaca or common outlet for the intestinal 
tube and urinary organs as in other fishes. 
The lateral openings on each side of the anus are still 
more curious and important, and merit the particular at- 
tention of the zootomist. These openings were recognised 
by Monro, and are mentioned by others ; but many have 
doubted their existence ; and from none have they received 
the attention to which their peculiar relations entitle them. 
