298 vishes. 



The superior part (No. (51 (a) much shorter than the other, is simple in 

 all the arches, excepting the first pair, which having no superior 

 pharyngean to support, is usually suspended to the cranium by a 

 small style (.Xo. 59) which we may. if we chose, consider the pharyn- 

 geal! of this pair. 



The two parts of the arch are joined together by a cartilage which 

 allows of movement, and form an angle which can be shut or opened 

 more or less. These arches are attached to the intermediate chain by 

 flexible cartilages so that the whole apparatus is movable, either open- 

 ing or shutting the angle formed by the two parts of the arch, thus 

 lowering or raising the back of the mouth, enlarging or narrowing 

 in a vertical direction, the space between the branchi. or by carrying 

 each arch more forwards or backwards, thus enlarging or narrowing 

 the intervals between the branchi that give the water exit. 



The external surface of the arches is hollowed for the lodgment of 

 the vessels, which furnish branches to the cartilaginous laminae 

 supported on this surface, these laminae constitute the essential part 

 of the organ o\ respiration. 



Their internal surface is furnished with small plates, cones, or bony 

 laminae, usually supplied with teeth, variously disposed according to 

 the species, the most general use of which is to arrest such bodies as 

 the fish swallows, prevent their being carried out with the water for 

 respiration, and entangle them in the intervals of the branchial 

 lamina 1 . These small pieces in their way. perform the same office, 

 as the epiglottis in Mammalia, or the indented edges of the larynx in 

 birds.* 



In our perch for example, the arches of the first pair have an 

 external row of these pointed and slender teeth like those of a rake, 

 and an internal row in the form of small plates : the following arches 

 have two rows of these little plates furnished with teeth like the pile 

 of velvet. 



Pharyngeal Bones, 



The Pharyngeal bones are situated at the entrance of the oesophagus, 

 immediately behind the branchial apparatus ; their office is to effect 

 a second mastication, often much more powerful than the first j for 

 this purpose they are furnished with teeth, which vary much in num- 

 ber and form, according to the species. 



In general there are two inferior and six superior. The inferiors 

 (No. 56)* are attached behind the branchi in the angle formed by 

 the two last arches ; they often form two triangular plates which 

 serves as a door for the pharynx : sometimes, as in the oyprins. they 

 are curved to surround a p .rt of the sophagus and somtimes as in 

 the labrus and seams, they are soldered into a single piece, or at least 

 they are united by immoveable suture. 



(a) The superior plureals of M. Geoffrey. 



* These small plates or indented points which cover the surfaces of these arches, 

 are called /radicals by M. Geoffrey, who looks vipou them as analogous to the rings 

 of the trachea. 



t M. Geoffroy calls them criceals. considering them analogous to the cricoid 

 cartilage. 



