PANCREAS. 



93 



in all. The appearance of the frill of pyloric 

 caeca is shown in fig. 67, and one of the 

 bunches separate in fig. 68. 



In the Salmon this apparatus of caeca is 

 much more voluminous. It is not condensed 

 around a particular portion of the intestine, 

 but extends linearly, from close to the duo- 

 denum for a distance of about eight inches 



along the intestinal wall ; each 



caecum opens 

 There is no 



by its own separate orifice. 



coalescence or fusion, so that 



the inside of the intestine there are seen as 



many orifices as caeca; they form a double 



row on each side, so that altogether there 



are four rows, and are arranged with the 



utmost regularity. The amount of secreting 



surface of these caeca 



some of them are ten 



big round as a tobacco-pipe; they rapidly 



on looking on 



must be very 

 inches long, 



great ; 

 and as 



Fig. 69. 



Portion of the alimentary canal of the Salmon ( Salmo //), 

 showing one double row of ctccal appetidayes and the pyloric 

 extremity of the other. 



a, oesophagus; b, stomach; c, pylorus; d, small intestine; 

 e, gall-duct. (One-third the natural diameter.) 



increase in length from the first three down- 

 wards, and the third from the stomach is 

 generally the longest. They then gradually 

 diminish, slightly in calibre, considerably in 

 length, to those furthest down the intestine, 

 which are pbout three inches long. Altogether 

 the secreting surface of these caeca must con- 

 siderably exceed that of the rest of the ali- 

 mentary canal, and the whole apparatus, taken 

 together, is next to the liver, by far the 

 largest of the viscera. Each double row con- 

 tains about thirty, so that altogether there 

 are sixty caeca, and as the average length of 

 each caecum is 6 inches, the whole length 

 of secreting surface must be 390 inches, or 

 upwards of 32 feet. 



In their internal ultimate structure these caaca 

 exhibit considerable variety ; in many the mu- 

 cous surface is closely laminated ; in some it is 

 covered with flattened, fused villi with 

 crypts thickly planted between their 

 bases. In the Herring (Jig. 70.) the 

 structure is very peculiar : on looking 

 vertically on the internal surface it is 

 seen to be mapped out into hexagonal 

 and pentagonal cells about -^ of an 

 inch in diameter, very evenly and geo- 

 metrically arranged, and each filled 

 with a mass of epithelium. The septa 

 between them appear to consist of sub- 

 mucous fibrous tissue, and on making 

 a section and looking at it laterally 

 they are seen to project between the 

 acervuli of epithelium, and rather 

 beyond them, and to have no epithe- 

 lial investment of themselves. The 

 masses of epithelium are seen to be 

 of a spheroidal form and very smooth 

 outline, though I could not distinguish 

 any basement membrane or capsule 

 wall of which they might be supposed 

 to be the contents, or any special 

 structure determining their outline. 

 I have thought this structure suffi- 

 ciently peculiar to give a figure of 

 it. A represents the appearance on 

 looking down on the surface; B, a 

 view of the wall in section, seen with 

 a lower magnifying power. 



Many anatomists deny the true 

 pancreatic nature of these pyloric 

 ca?ca, and assert that many fish pos- 

 sess, over and above them, a true 

 glandular pancreas, analogous in struc- 

 ture to the pancreas of higher animals. 

 Weber first described such an organ 

 in the carp, as interlaced with the 

 lobules of the liver, anil, so to speak, 

 confounded with them, but having a 

 proper excretory canal opening into 

 the intestine by the side of the cystic ; 

 he also thought that he had seen 

 traces of a pancreatic duct in the 

 pike. Much more recently Alessan- 

 drini described the same exircting 

 duct, as also the volume and position 

 of the pancreas, in the same fish. 

 In the Siiurus glanis MM. Brandt and 

 Ratzebourg have taken for the pan- 



