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Show 670 PROF. G. B. HOWES ON THE VISCERAL [Dec. 2, by a deep constriction (Plate LVII. figs. 1 & 4) which coincides with the point of origin of a very efficient pyloric valve (v, fig. 4). I have elsewhere shown1 that in the Thornback (Raia clavata) the left kidney may be restricted to the posterior third of the body-cavity, and that the conditions of its displacement show the same to have resulted either from atrophy or concentration in accommodation to the enlarged stomach and spleen. That which may be thus true of the individual Thornback is true of certain other species of the genus Raia, and of the fish now under consideration ; so completely so in the latter that the entire kidney may be seen from beneath (re, fig. 1) while tbe stomach is still in its natural position. Between the liver and stomach of this fish there passes a well-defined lesser omentum (om., fig. 1) ; the suspensory ligament of the liver (lg.) is very extensive and asymmetrical, passing on the left side to the dorso-lateral wall of the cardiac gastric sac (cd.), and on the right to the adjacent body-wall and head of the testis (ts. oi fig. 2). Buried up in this ligament there lies the customary vestige of the coalesced ostia of the Mullerian ducts (d.m., fig. 1), and that here assumes the form of a short but spacious tube, disposed obliquely on the right side, and closely bound down to the ventral body-wall. There is no trace of median ventral mesentery. The pyloric chamber of the stomach of this fish is long aud tubular (py., figs. 1 & 4), and, as already stated, marked off from the head of the small intestine by a deep constriction. That portion of it which lies to the right of the axial line is skirted posteriorly by a pancreas, which, contrary to the general rule among these fishes, is lozenge-shaped (pc, fig. 4). The Bursa Entiana (i.s.') is remarkable for its subdivision internally into two chambers, the posterior of which receives the bile-duct (d.h.)2; this subdivision is effected by a crescentic infolding of the postero-lateral wall to form a well-defined intra-duodenal valve (v."). That which is most noteworthy in the general disposition of the viscera of this fish is the non-appearance of the processus digitiformis and spleen, when the parts are viewed from the ventral aspect. The appendix digitiformis of all other Elasmobranchs lies conspicuously disposed at or towards the left side of the valved intestine3. The spleen of the Plagio-stome fishes is very variable in its extent and relationships ; it lies either (most Batoids) in the bay formed by the cardiac and pyloric gastric sacs, or in a more or less close relationship to the base of the entire stomach. The relations of these organs are, in Hypnos, remarkable and exceptional, as the sequel will show. The alimentary viscera of the Plagiostomi are well known to be suspended by two folds of mesentery-an anterior one, which is continuous in front with the suspensory ligament of the liver; and a posterior one, which serves to attach the processus digitiformis 1 Journ. Anat. & Phys. vol. xxiv. (N. S. vol. iv.) p. 407 (1890). 2 The bursa was injured at the point of termination of the pancreas anteriorly, wherefore it was not possible to determine the course of the pancreatic duct. L 'J Cf. Blanchard, Mittheilung. a. d. Embryol. Instit, Wien, Heft iii. p. 190 (1878-79). |