BREATHING MECHANISM OF THE LAMPREYS. 7 



pharynx. Here between the pharyngeus muscle and the mucous 

 lining of the cavity on its lateral walls are stretched two mus- 

 cles, the hyomandibulari-semiannularis and the hyomandibulari- 

 glossus. These muscles cause the mucous membrane to project 



FIG. 4. Dorsal side of the head of P. marinus dissected to show the muscles over- 

 lying the pharynx arid oesophagus. <?, basilaris muscle ; (>, supporting cartilage ; 

 c, pharyngeus muscle ; d, raphe of pharyngeus muscle ; e, gill sac ; f, oesophagus ; 

 k, posterior pharyngeus. 



into the cavity in the form of a longitudinal ridge on each side. 



