232 



ZOOLOGY 



SECT. 



pror-b 



art 



FIG. 855. Ceratodus Forsteri. Dorsal view of the 

 skull. A, anterior median membrane-bone ; art. articular 

 surface for second fin-ray ; B, posterior median membraiie- 

 bone ; C, inner lateral membrane-bone ; lab. labia car- 

 tilages ; lam. process projecting over gills ; op. oper- 

 culum ; pr.orb. pne-orbital process of chondrocraniuni ; 

 sb. orb. sub-orbital bones sq. squaniosal. (After Huxley.) 



the branchial region 

 Imbedded in the car- 

 tilage of the posterior 

 part are a small pair 

 of exoccipital ossifica- 

 tions. On the upper 

 surface two unpaired 

 (A and !>) and four 

 paired ((7and>S^) mem- 

 brane-bones overlie the 

 cartilage : and on the 

 ventral surface is a 

 large membrane-bone 

 (Fig. 856, P. spfc.) re- 

 presenting the para- 

 sphenoid of the Tele- 

 ostomi. Rudimentary 

 vomers (Vo.} support 

 the vomerine teeth In 

 front is a pair of small 

 upper labial cartilages. 

 Apalatoquadrate carti- 

 lage (pal.} firmly fixed 

 to the side-wall gives support to the mandible, and seems to contain 

 representatives, not only of the palatine, pterygoid and quadrate, 



but of the hyomandibular and 

 symplectic of the Teleostomi. 

 In front it contains a palato- 

 pterygoid ossification. Behind 

 it a small cartilage immovably 

 fixed to the side-wall of the 

 skull is probably the opercular 

 cartilage. One of the two 

 lateral membrane-bones ($<?) 

 situated over the palato-quad- 

 rate is the squamosal. Opercu- 

 lar (op.) and interopercular (int.) 

 bones support the operculum. 

 The hyoid (hy.) and branchial 

 arches (br.) are cartilaginous. Of 

 the latter, four are completely 

 developed, each consisting of a 

 dorsal and a ventral cartilage ; a 

 fifth is represented by a rudi- 

 ment attached to the fourth. 



The pectoral arch (Fig. 854, 

 vet.) is a stout cartilage with a 



FIG. 856. Ceratodus Forsteri. Ventral 

 view of the skull, c, occipital rib ; >, 

 palatine teeth ; </', vomerine teeth ; na. 

 anterior and posterior nares ; P. palatine 

 region of palato-pterygoid ; 7'. */>/<. para- 

 sphenoid ; Pt. pterygoid ; Qf. quadrate 

 region ; Vo. vomer. (From Dean, after 

 Gimther.) 



