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 pyloi'ic valve (v, fig. 4). 



I have elsewhere shown ^ 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 the 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 {Ig.) 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. of 

 fig. 2). Buried up in this ligament there lies the customary vestige 

 of the coalesced ostia of the Miillerian 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 and 

 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 re- 

 markable for its subdivision internally into two chambers, the 

 posterior of which receives the bile-duct {d.h.)'; 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 intestine^. 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 



' Journ. Aiiat. & Phys. vol. xxiv. (N. S. vol. iv.) p. 407 (1890). 



^ The bursa was injured at the point of termination of the pancreas ante- 

 riorly, wherefore it was not possible to determine the course of the pancreatic 

 duct. 



^ Cf. Blanchard, Mittheilung. a. d. Embryol. Instit. Wien, Heft iii. p. 190 

 (1878-79). • ■ 



