Ill INTESTINAL TRACT. 



between which a cardiac constriction is not so frequently observable as a 

 change in the structure of the lining mucous membrane. In some forms there 

 hardly exists any definite line of demarcation between the lower end of the 

 stomach and the commencement of the small intestines, but in many a 

 constriction occurs in this situation, termed the pylorus, although it must 

 be observed that the orifices at the ends of the stomach are usually more or 

 less approximated, in order that the food may be retained as in a ccecum. 

 Occasionally the stomach occurs not in the direct course of, but to one side as 

 it were, of the intestinal canal. A second constriction, marked internally by 

 a more or less well-defined internal valve, shows where the small intestines 

 terminate and the large ones begin. 



Generally among teleosteans the various portions of the intestinal tract 

 are sufficiently distinct to be distinguished simply by an external inspection : 

 'sometimes the differences between each part are so slight that the situation 

 where the ducts enter give the best clue to the various parts. 



If the intestinal canal is slit up and its inner surface examined, the 

 commencement of the stomach is generally observed to be defined by 

 increased vascularity and a more delicate lining membrane than that existing 

 in the oesophagus. Its upper or cardiac orifice is usually larger than its 

 lower or pyloric one, while the form of the entire organ is subject to 

 considerable modification, being usually found in one of the two following 

 divisions : the siphoned, which somewhat resembles a bent tube, as seen in 

 the lumpsucker, flounder, salmon, carp, sturgeon, and most of the plagios- 

 tomes ; and the ccecal, in which it ends in a blind sac, and the pyloric portion 

 is continued from its right side, as observed in the perch, gurnard, weevers, 

 John Dory, whiting, &c. An intermediate or transitional form sometimes 

 exists, as in the sea scorpion or the turbot, irrespective of which certain 

 deviations occur which it is not my purpose to enlarge upon-. The Indian 

 Scicena, eironeously termed " whiting" (Johniiis), has the pyloric portion of 

 its stomach muscular, but this augmented thickness of the muscular coats 

 may be best perceived in the mullets (Mugil), in which the cardiac portion is 

 continued downwards into a blind sac, while the pyloric portion is thickened 

 like the gizzard of a bird, appearing as a rounded or conical projection 

 externally, and which when cut into is found to consist of thick muscular walls, 

 the small cavity remaining internally being lined with a thick and horny 

 epithelium. This gizzard-like stomach is evidently employed for grinding 

 up hard food, audit is curious to observe how, when some fresh-water forms 

 select hard substances for their diet, the coats of their stomachs may likewise 

 become thickened. Thus in the gillaroo trout we find the ascending or 

 pyloric portion of the stomach thickened. In the cyclostomes and 

 leptocardii the intestinal tract is straight, but in the lampreys longitudinal 

 folds are present in the oesophagus, and a single one along the intestinal tube. 



