ELEVEN TAR Y ANA TOMY. 



[LESS. 



The gill-chamber is further protected by a membranous 

 fold which lies within the opercular flap. This fold is the 

 branchiostegal membrane, and is supported by the bmti- 



FIG. 403. LEFT BRANCHIAL ARCHES OF PERCH. (After Cuvier.) 



i, glosso-hyal ; 2, 3, and 4, basi-branchials ; 5, hypo-branchials ; 6, cerato-bran- 

 chials ; 7. epi-branchials ; 8, styliform pharyngo-branchial ; q, pharyngobran- 

 chials ; 6 , inferior pharyngeal bone ; g and 9", superior pnaryngeal bones ; 

 5, 6, 7, and 8, first branchial arch ; 5', 6', 7', and 9, second branchial arch ; 5", 

 6", 7", and 9', third branchial arch ; 5", 6'", and 7'", fourth branchial arch ; 

 6'"', fifth branchial arch (inferior pharyngeal bone). 



cJiiostegal rays, which (like the membrane itself) are attached 

 to the post-axial side of the hyoidean arch. 



The respiratory surfaces of the gills are supplied with 

 water by the mouth, which continually takes in fresh supplies, 



FIG. 404. SKULL AND BRANCHIAL ARCHES OF A SHARK. 



b 1 35, branchial arches ; h, hyoidean arch; m, mandible ;pq, palato-quadrate arch. 



(From the College of Surgeons Museum) 



such supplies passing out, in the osseous Fishes, from the 

 common opening behind the operculum ; and, in the Elasmo- 

 branchs, from each separate aperture of the successive gill- 

 chambers. 



