78 



ANATOMY OF VERTEBRATES. 



(Narcine), and at the same time with distinct pterygoid 



cartilages. 1 



Four or five short cartilaginous rays diverge from the posterior 



margin of the tympanic pedicle, ib. c, and support a membrane 



answering to the opercular nap in Osseous fishes ; in their ultimate 



homology these rays are the skeleton of the diverging appendage 



or limb of the tympano-mandibular arch. 



The hyoid arch in Squatina, as in most other Plagiostomes, 



consists of two long and strong cerato-hyals, and a median flat- 

 tened symmetrical piece, 

 the basi-hyal. Six short 

 cartilaginous rays extend 

 outwards from the back 

 part of the cornua, support- 

 ing the outer membranous 

 wall of the branchial sac : 

 these answer to the bran- 

 chiostegal rays in osseous 

 fishes, and support the di- 

 verging appendage or limb 

 of the hyoidean arch. But 

 the fold of integument in 

 which they project is not 

 liberated, and is continuous 

 with that supported by the 

 opercular rays from the 

 tympanic pedicle. Five 

 branchial arches, fig. 30, 

 i, 2, 3, 4, 5, succeed the 

 hyoidean ; but are sus- 

 pended, as in the Lam- 

 prey, from the sides of the 

 anterior vertebra? of the 

 trunk. In the Sea-hound 

 (Scymnus lichia),ftg. 63, the 

 ceratobranchials, f, f, and 

 basibranchials, e, e, are 

 shown, with the frame- 

 work of the gills, f/, i. Be- 

 hind these arches is the sca- 



pulo-coracoid arc, 52, united by cartilaginous confluence at the 



mid-line, not by ligament as in the Sturgeon. 



1 xxi. 1 835, pi. v. figs. 3 & 4. It ma)' be questioned whether the detached plate, 

 called palatine by Dr. Henle, be not rather the entopterygoid. 



Skull with branchial and scapular arches, Scymnus. xliii. 



