BREATHING MECHANISM OF THE LAMPREYS. 5 



rior lobe are thus brought into the same plane as the central 

 teeth of the funnel and function with them m rasping. The great 

 freedom of movement of the end of the tongue necessary in rasp- 

 ing is attained by its central cartilage (Fig. I , c') being attached 

 by a sort of socket joint to the enlarged anterior end of the large 

 lingual cartilage (Fig. I, ). 



The mouth cavity is short and curved, about five times as long 

 as it is wide at its middle, and extends from the oral funnel to 

 the pharynx, a distance of about 2 cm. Its anterior end, where 

 it meets the funnel, is larger than in any other part. Its roof and 



FIG. 3. Diagram of the arrangement of the teeth in the oral funnel of P. marinns. 

 The heavy lines show the loops upon which the teeth are inserted. 



sides are dome shaped and are formed by the semiannularis car- 

 tilage in front and by the semiannularis muscle behind (Fig. I, r, 

 c]. The muscle arises from the posterior border of the cartilage 

 and forms a very small portion of the roof of the mouth. The 

 posterior portion of the dome formed by the semiannularis mus- 

 cle arches so close to the ventral wall of the mouth that it greatly 

 constricts the cavity in this region and when it contracts, com- 

 pletely shuts off the mouth cavity from the pharynx. The floor 



