PHARYNX 



(S. 5.439)137 



Pharynx 



The six powerful lips arch together over a large characteristic 

 pharynx, consisting of a rather simple, ellipsoidal or elongated cavity, 

 whose cross-section is more or less irregularly circular, and of which 

 there are two distinct types. 



Types of Maw. Teeth. In one type, characteristic of the larger 

 species, there are longitudinal ribs, sometimes simple, sometimes duplex, 

 situated mainly on the median and submedian 

 lines (subgenus lotonchus). 3 When these lon- 

 gitudinal ribs are well-developed there is a 

 tendency for the dorsal tooth or onchus to be 

 farther back, and for the submedian teeth, 

 smaller still, to be located toward the base of 

 the pharynx, and in extreme cases all three 

 teeth may be located actually at the base of 

 the pharynx, or indeed be quite vestigial. The 

 farther back the teeth, the smaller they are, 

 and when located actually at the base of the 

 pharynx they are often exceedingly small. 



In the other type of pharynx the dorsal 

 tooth is usually strongly devel- 

 ^pk, M oped, and is located midway or 

 fj H farther forward ; in which case 



X750 



FIG. 6. Dorsal view of the 

 throat of M. muscorum, to 

 show the arrangement of den- 

 ticles (dnt.) characteristic, of 

 the subgenus Prionchulus; 2 they 

 constitute a rude "saw." Com- 

 pare with Fig. 7. 



o 



the wall of the pharynx is strongly reinforced along the dor- 

 sal line, while the submedian longitudinal ribs are lacking, 

 or at any rate are faint. However, there often occurs on 

 each of the two ventrally submedian lines in this type of 

 pharynx an onchus of smaller size, located a 



little farther back than the main onchus ; ex- 

 ceptionally these submedian onchi may be 

 nearly as large as the dorsal onchus. In 

 several species the onchi are retrorse (sub- 

 genus Anatonchus 5 } , and when of this char- 

 acter are sometimes more slender, even some- 

 what digitate. 



Fangs. Denticles. The onchi act as fangs, 

 and are used in conjunction with the power- 

 ful lips in seizing and holding the prey. In 

 these maneuvers they are aided by minor 

 pharyngeal structures, prominent among 

 which in some species are two submedian 



'lotonchus, insignificant tooth; 4 Prionchuhis. a small saw-tooth; B Anatonchus, reversed tooth. 



FIG. 7. Above, profile and front 

 view of the same series of denticles 

 in the throat of M. muscorum. Be- 

 low, two cross-sections of the same 

 specimen, showing end view of the 

 same denticles; at left the section 

 is through the dorsal tooth (shown 

 black) ; at right the section is above 

 the tooth. The denticles are shown 

 in the upper part of these two lower 

 figures. The two joints shown in cross- 

 section impart a slight degree of 

 mobility to the pharyngeal walls. 

 Compare with Fig. 6. 



