Page:The Zoologist, 1st series, vol 1 (1843).djvu/117

Rh cuticular investment terminates suddenly at the part corresponding to the cardiac orifice of the stomach. It is exceedingly muscular, and its parietes are nearly half a line in thickness; the fibres run principally in a longitudinal direction, by which means the interior is thrown into a number of longitudinal rugæ, circular fibres are however very conspicuous in some parts: some of the longitudinal fibres appear to be inserted into about half the base of the cartilaginous jaws. The separate fibres, when examined with a power of 400 linear, are found to exceed greatly in size those of the muscular tunic, and, like them, they are remarkable for their dotted appearance, (fig. e and f, p. 92). The stomach is nearly cylindrical in shape; its parietes are thin and easily lacerated, it is slightly constricted at intervals of about a quarter of an inch, at which points it appears to be firmly connected by membranous septa to the walls of the abdominal cavity; it expands a little at its lower third, just before it joins the large intestine or rectum, which appears, as far as size is concerned externally, to be nothing more than a continuation of the stomach.

The cœca are given off from the lower portion of the stomach, one on each side; they are little more than half an inch in length, and about a line in diameter: in some specimens these cœca are larger at their blind extremities than in the middle, in others they gradually diminish in size from their point of connexion to their free extremities: in their natural position they are firmly bound down by cellular tissue to the sides of the rectum. Unless the animal be dissected in water, these cœca may easily be overlooked. The rectum is of a conical figure, being broad above, where it is connected with the stomach, and small below, where it forms the anal outlet, which opens externally on the dorsal surface of the animal immediately above the sucking disk. It varies from three quarters to an inch in length, and is about a quarter of an inch in diameter at its broadest part.

The interior of the œsophagus, as has been stated, is of a white colour, and is thrown into longitudinal rugæ; it is lined with a cuticle of a white colour, which ceases abruptly at the cardiac orifice of the stomach, where there is a constriction; from the muscular fibres being irranged principally in a longitudinal direction, it is capable of considerable dilatation, in which it differs much from the same part in the medicinal leech. The interior of the stomach is of a red colour, and consists of wavy folds of mucous membrane; it appears to be quite free from villi, but the intestine with which it is continuous is largely supplied with them: there is a tolerably well developed constriction or pyloric valve at the junction of the stomach and intestine. The