XII 



PHYLUM CHORDATA 



opening of the mouth is situated. There are no jaws, but 

 on the inner surface of the buccal funnel and on the tongue 

 a fleshy (?) process below the opening of the mouth. In 

 Myxine the funnel is edged with slender, flexible processes 

 or tentacles. At the sides of the head are the eyes, well 

 developed and conspicuous in the lamprey, imperfect and 

 buried beneath the skin in Myxine, and on the upper surface 

 is a single median aperture, the nostril. Further back at 



na.ap 



FlG. 221. Petromyzon marimiS. Ventral (A), lateral (B), and dorsal (C) views 

 of the head. br. cl. /, first gill-cleft; buc.f, buccal funnel; eye, eye; mth, mouth; 

 na. ap, nasal aperture; /, papillae : pn, pineal area; 1. I, t. 2, t. 3, teeth of buccal 

 funnel; /. 4, teeth of tongue. (After W. K. Parker.) 



the sides of the head are, in the lamprey, a series of seven 

 pairs of slits, the gill-slits, leading to the gill-pouches ; in 

 Bdellostoma there are six pairs of small gill-slits, in Myxine 

 only a single aperture on each side. 



The skeleton is very unlike that of the true fishes, and 



