DIGESTIVE SYSTEM OF FISHES, 229 



anterior jaws were compelled by their services to respiration to leave 

 unfinished : and thus the mouth of typical fishes is closed at both 

 ends by dentigerous jaws. 



The first jjortal to the alimentary tract is usually formed by the 

 upper and lower jaws {fig. 61. a, b), and their teeth; the Gym- 

 nodonts* are so called on account of their conspicuous manifestation 

 of tliis character. But in some Fishes the arched and fortified barrier 

 is preceded by a fosse inclosed by fleshy lips : the whole genus Lahrus 

 owes its name to this peculiarity ; the Carp-tribe (Q/pr««it?«) also 

 have it ; and, in some of them, the labial organs are developed to ex- 

 cess, as, for example, in the genus thence termed La heobnrb us, in which 

 the lips are not only unusually thick and fleshy, but the lower one is 

 produced dowuAvards like a pointed beard. The labiated Fishes 

 have not, however, so distinct a 'sphincter oris' as Mammals, Many 

 Fishes, especially those of the Cyprinoid and Siluroid families, 

 have fleshy and sensitive barbs or tentacles in the vicinity of the 

 mouth, and subservient to its functions ; those of the Siluroids being 

 supported by bony or gristly stems. Tentacles depend from the 

 rostral prolongation of the Sturgeon, and from the mandibular sym- 

 physis of the Cod, The Lepidosiren and Cod have fringed processes 

 or filaments between the teeth and lips, which seem designed to 

 assist in testing and selecting the food. IVIi*. Couch f narrates an in- 

 stance of a large Cod, in good condition, taken on a line at Polperro, 

 Cornwall, in which the orbits contained no eyeballs, but were covered 

 with an opake reticulated skin. So that he felt convinced that " eyes 

 never had existed ; " yet the fish was in good condition, and must 

 have depended on the tactile organs about the mouth for the discovery 

 of its food. 



The edentulous Sturgeon is compensated by a produced cartila- 

 ginous snout, with which it upturns the mud in quest of food at the 

 bottom of the rivers it frequents. The allied Spatularia, in which a 

 minutely shagreencd surface on the jaws represents the whole dental 

 system, has had the force of development of subsidiary organs of ali- 

 mentation expended in the production of the still more remarkable 

 rostrum (fig. 61. y.), which is broad and flat, like the mandible of a 

 spoonbill, and is more than half the length of the entire body. 



The conical lip of the suctorial Myxinoids sends off' from its ante- 

 rior expanded border six or eight long tentacula : the inner surface of 

 the lips is beset with short branched tentacles in the Aramocete : 

 the Lancelet has more simple, but highly vascular intra-buccal 

 processes {fig. 46, g g), and the vertically fissured aperture of its 

 mouth is provided on each side with a series of long slender jointed 



* Gr. (/»w«os, uncovered ; of/oMS, tooth. t X'"viu. p. 72. 



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