Chap. IX.] BUCCAL ELEMENTS OF SKULL. 327 



for their support. Throughout the series, whether 

 gills are present or not, the first two take on, in addi- 

 tion or solely, quite another than a branchial function. 

 These (Fig. 137 ; Mrc, ny) send off from their 

 upper end a process, which is directed forwards ; the 

 anterior arch becomes segmented into an upper and a 

 lower piece, both of which, growing forwards, form 

 the rudiments of the upper and lower jaws. The 

 former (pi, Pt) may be called the pterygo-quadrate 

 bar, the lat- 

 ter the Mec- 

 kelian car- 

 tilage. The 

 chief means 

 of connection 

 bet ween these 

 bars and the 

 cranium is , 



not the me- / TOT v , ; R j 

 tapterygo- Tf Mn ***/ J 



idal region, Fig i 37 ._Head of Embryo Dogfish (11 lines long) . 



Or hinder and T?% Trabecula ; Pi, Pt, pterygo-quadrate ; m, Pt, rneta- 



e> pterygoid ; M?t, inandibular cartilaee ; ny, hyoid arch ; 



Upper part OI sr l, first branchial arch, with four succeeding 



,1 /> -i arches; sp, mandibulobyoid cleft; cl, hyo-lmtnchial 



the first arch, cleft; Ci,c2,c3, cere bral vesicles. (After Parker.) 



but the upper 



part of the second arch (H?/), which forms the Ityo- 



mandibular. 



In such a skull, then, as that of the dogfish (which 

 has formed the basis for this account), the attachment 

 of the jaws to the skull is hyostylic (Huxley) ; in a 

 large number of fishes this hyostylic arrangement 

 obtains ; in a few (Notidanus), however, the meta- 

 pterygoid does enter into contact with the cranium, 

 and the jaw is then supported by elements of both the 

 inandibular and hyoid arches, or is ampliistylic. On 

 the other hand, in Chimsera, the Dipnoi, and all the 

 pentadactyle Vertebrata, the hyoid takes no share in 



