PISCES. 



981 



of the skeleton., and a series of deep alveoli 

 is excavated in each of its lateral margins (jig- 

 518). 



The teeth which are lodged in these sockets 

 are elongated, compressed in the same plane 

 as that of the body of the saw, and their edges 

 converge to a sharp point, which is situated a 

 little behind the axis of the tooth. Each ros- 

 tral tooth is solid, its base being slightly con- 

 cave and porous like the section of a cane, bul 

 the pores are finer and more numerous. The 

 walls of the socket are formed by ossification 

 of the rostral cartilages to an adequate extent; 

 but as unnecessary weight under any circum- 

 stances, but especially at the fore-end of the 

 lish, would be a cumbrous impediment to its 

 motions, the spaces intervening between the 

 sockets are hollow and filled with a gelatinous 

 medulla. A large vascular canal traversed by 

 brunches of the facial artery and of the second 

 division of the fifth pair of nerves enclosed 

 in a cellular gelatinous tissue, rwns parallel 

 with the axis of the saw along the back part of 

 the alveoli, and supplies the materials for the 

 increase of the teeth, winch are not shed and 

 renewed like the maxillary teeth, but grow 

 with the growth of the body by constant 

 addition of fresh pulp-material progressively 

 ossified at their base. 



(Emip/i'gm. Owing to the extreme short- 

 ness of the passage between the cavity of the 

 month and the stomach, the length of this tube 

 is extremely limited in the whole race of Fishes; 

 nevertheless, occasionally its boundaries are 

 well marked, and its structure sufficiently dis- 

 tinct from that of the alimentary canal to entitle 

 this part of the digestive apparatus to a brief 

 notice. Its walls are generally strong and 

 muscular for the purpose of passing the food 

 into the stomachal cavity, but more especially 

 so in those voracious Fishes which swallow 

 dense and indigestible shells of various kinds, 

 or that are subject to have their stomachs 

 loaded with the hard bones of digested fishes, 

 all which materials are in such instances regur- 

 gitated and thrown out of the mouth much after 

 the manner of the "castings" of the Hawk or 

 Owl among birds of prey. In a few races, how- 

 ever, the oesophagus exhibits peculiarities of 

 structure that are remarkable. Thus in the 

 Torpedo and others of the Kay genus, there is 

 a very thick layer of a soft and semi-gelatinous 

 substance interposed between the lining mem- 

 brane and the muscular coat, the use of which 

 it is by no means easy to conjecture. In the 

 Sturgeon the mucous membrane of the gullet 

 is prolonged into transverse valvular folds, 

 analogous in their nature to the conical pro- 

 cesses found in that of the Turtle. But the 

 most striking example of a valvular apparatus 

 situated in this part of the digestive tube is met 

 with in the Sharks (jig. 519), in which race 

 of Fishes the termination of the oesophagus is 

 indicated by a great number of long fleshy 

 stems, which divide and subdivide into very 

 numerous branches, and thus form a dense and 

 prominent fringe hanging loosely downwards 

 towards the stomach, in such a way as to allow 

 anything swallowed to pass freely in that direc- 



tion, but by the interlacement of the fringes 

 effectually preventing anything from returning 

 towards the mouth. This structure is most 

 conspicuously seen in the great Shark (Sijualua 

 maximus), in which species, owing to the com- 

 parative smallness of the teeth which arm the 

 jaws, it is extremely probable that many Fishes 

 are swallowed alive and might retain their vita- 

 lity sufficiently long to struggle back again out 

 of the stomach of their devourer, did not this 

 strange gate effectually bar their progress. 



Stomach. This viscus is, in the generality of 

 species, a musculo-membranous bag of very 

 simple structure and of variable shape in diffe- 

 rent genera. Sometimes, however, its muscular 

 walls are sufficiently strong to perform to a certain 

 extent the functions of a gizzard : this seems to 

 be the case, for example, in the Gillaroo Trout 

 (Sulmo fario), and to a far more remarkable 

 extent in the Mullets (M/tgil), in which the 

 oesophagus terminates inferiorly in a deep cul- 

 de-sac that serves the purpose of a crop. The 

 muscular stomach or gizzard opens from one 

 side of this cesophageal bag, to which it is 

 attached at right angles. Its shape is pyriform, 

 the narrow end being directed towards the in- 

 testine, and its muscular walls nearly half an 

 inch thick. Internally it presents numerous 

 longitudinal folds, all covered with a thick cu- 

 ticular lining, and evidently the whole appara- 

 tus is very analogous to the true gizzard of 

 a granivorous bird. It was John Hunter's 

 opinion that neither of these can be justly 

 regarded as gizzards, since they want the most 

 essential characters, namely, a power and mo- 

 tion fit for grinding, and a horny cuticular 

 lining. According to Professor Owen, how- 

 ever, the latter structure exists in the gizzard of 

 the Mullet as a distinct layer of rough and 

 easily separable cuticle. The stomach of the 

 Gillaroo or Gizzard-trout is certainly, as de- 

 scribed by Hunter, more globular in its shape 

 than that of most Fish, and endued with suffi- 

 cient strength to break the shells of small shell- 

 fish, which is probably accomplished by having 

 more than one in the stomach at a time, and 

 also by taking pretty large and smooth stones 

 into the stomach, which will answer the pur- 

 pose of breaking, but not so well that of grind- 

 ing ; nor will they hurt the stomach, as they are 

 smooth when swallowed ; but this stomach can 

 scarcely possess any power of grinding, as the 

 whole cavity is lined with a fine villous coat, 

 the internal surface of which appears every- 

 where to be digestive. The common stream- 

 trout, which only differs from the "Gillaroo" 

 in having the walls of its stomach not so thick 

 by two-thirds as the other variety, likewise 

 swallows smooth round stones wherewith to 

 crush the shell-fish which it occasionally de- 

 vours. 



Intestinal canal. The intestines of Fishes 

 present as many variations as regards their rela- 

 tive length when compared with that of the 

 body, as do those of any of the higher Verte- 

 brata, but their general arrangement is of a 

 much more simple character. In the Flying- 

 fish (" K,ni<T//<.s-J, indeed, it presents the sim- 

 plest possible form, being merely a straight 



