252 FISHES CHAP. 
on the jaws.”* Pharyngeal teeth differ greatly in size and 
structure in different Teleosts, and, like the jaw-teeth, they are 
capable of replacement by vertical succession. The teeth are 
sometimes restricted to the inferior pharyngeal bones (cerato- 
branchials of the last branchial arch), and then, as in the Carp 
(Cyprinus), they may bite against a callous pad on the under 
surface of the basioccipital bone; or, as In some of the Wrasses 
(Labrus), the inferior teeth are opposed to superior teeth on the 
upper pharyngeal bones (pharyngo-branchials of more or fewer 
of the branchial arches). When pharyngeal teeth are present 
it is probable that they are the principal masticatory organs, the 
jaw-teeth being used for seizing or holding the prey. 
Alimentary Canal. 
A protrusible tongue is never developed in Fishes. A rudi- 
ment of that organ is present in the Elasmobranchs (Fig. 153) 
and Dipnoi, and also in the Crossopterygii, and usually consists 
of an elevated area of mucous membrane provided with free 
lateral edges and a forwardly projecting apex; it is supported by 
the basi-hyal element of the hyoid arch. In the Crossopterygii 
(e.g. Polypterus) the tongue contains muscle fibres, and in the 
Dipnoi, where the organ is better developed thaa in any other 
Fishes, special lingual muscles are present. 
The pharynx succeeds the oral cavity, and is perforated on 
each side by the branchial clefts (Figs. 153, 154). The rest of 
the alimentary canal differs considerably in various Fishes in 
the degree of distinctness of its several regions, and in the 
extent to which it is convoluted. As a rule the pharynx is 
followed in succession by an oesophagus, a stomach, and an 
intestine (Fig. 1535), the latter terminating in a portion usually 
termed the “rectum.” The boundaries of these regions are not 
always very obvious, but are indicated by variations in calibre, 
by changes in the character of the lining epithelium, by special 
valves or sphincter muscles, or by the entrance of the ducts of 
certain glands lke the pancreas and liver. The oesophagus is 
occasionally separated from the stomach by a slight constriction, 
but more frequently the replacement of the squamous epithelium 
of the oesophagus by the columnar epithelium of the stomach 
1 Ridewood, op. cit. p. 390. 
