[chthyopsida 



417 



^vlv.v. 



<t <f a a it. 



crt.pal-qd) 



le'thor. 



crt.md. 



Fig. 322. Breathing valve of a skate. (1) Lower jaw removed; ventral view of 

 upper jaw and roof of mouth. (2) Dorsal surface of the detached lower jaw. (3) 

 Parasagittal section at position indicated by x—x in (1). (cav. or.) Oral cavity: 

 (crt. md.) mandibular cartilage; (crl. pal-qd.) palatoquadrate cartilage; (e'th. or.) 

 oral epithelium; (na.) nostril; (spr.) internal opening of spiracle; (vlv. d.) dorsal flap 

 of breathing valve; {vlv. v.) ventral flap of breathing valve. 



