24 CLASS XIV. 



it fast, than for dividing it. In form and number they present 

 much variety in this class. In some fishes, as in the genus Acipenser, 

 Syngnathus, &c. the teeth are entirely absent; in others, as the 

 pike, they exist in great numbers in the lower jaw, the intermax- 

 illary bone, the vomer, the palate-bones, the tongue, the branchial 

 arches and the pharyngeal bones. Teeth are rarely met with in 

 the two upper jaw-bones that lie in the lip. The form is very vari- 

 ous, sometimes that of laminae, mostly that of a cone, much like the 

 corner teeth of mammals. Sometimes the teeth are as fine as hairs, 

 as in the genus Chcetodon. The mode of attachment differs, yet 

 only seldom are they contained in sockets; ordinarily they are 

 united to the bones by ligamentous matter alone or are coalescent 

 with them by ossification. They are usually renewed constantly, 

 and a regular replacement of teeth that occurs only once is met with 

 in the mammals alone 1 . 



Salivary glands are not met with in the class of fishes. As a 

 rule, these organs are more largely developed in animals that live on 

 vegetable food than in those that make use of animal food ; fishes 

 live mostly on the last. Saliva also may more easily be dispensed 

 with where no mastication is performed, and the food, as in fishes, 

 is rapidly swallowed. There are, however, as in the sharks and 

 rays, under the palate acinous glands, which secrete a slimy fluid; 

 but these cannot be regarded as homologous with salivary glands. 

 As little is there any excretory duct to the structure which in the 

 carp is situated under the skull, in front of the ossa pharyngealia, 

 which by some has been looked on as a salivary gland 2 , and of 

 which the strong contraction under the action of various irritants 

 has been announced by WEBER and MUELLER 8 . 



The tongue in most fishes is small, and possesses slight mobi- 

 lity. The oesophagus commences like a funnel in the wide cavity 



1 For obtaining a well-grounded knowledge of the teeth of fishes, the accurate and 

 comprehensive work of R. OWEN", Odontography, London, 1840 1845, 8vo, pp. i 178, 

 must be referred to. 



2 H. RATHKE Beitrdge zur Geschichte der Tkierwelt, n. Halle, 1824, 4to, s. i 7. 

 Such a spongy tissue RATHKE found not only in Cyprinus, but also in Cobitis, Silurus, 

 Belone, &c. (very small in the last-named genus) ; he is of opinion that it occurs uni- 

 versally in those (osseous) fishes that have no appendices pyloricce. 



3 E. H. WEBER, in MUELLER'S Archiv fur Anat. u. Physiol 1827, s. 308311, 

 regards it as an organ of taste. MUELLER found in it animal muscular fibre. Physiol. 

 n. 35- 





