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 ; wn, 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 (p/, ft) may be called the pterygo quadrate 

 bar, the lat- 

 ter the Meo 

 kelian car- 

 tilage. The 

 chief means 

 of connection 

 between these 

 bars and the 

 cranium is 

 not the me- 

 tapterygo- 

 idal region, 

 or hinder and 

 upper part of 

 the first arch, 

 but the upper 



part of the second arch (ny), which forms the hyo- 

 maiidibular. 



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 liyostylic (Huxley) ; in a 

 large number of fishes this hyostylic arrangement 

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

 pterygoid does enter into contact with the cranium, 

 and the jaw is then supported by elements of both the 

 mandibular and hyoid arches, or is amphistylic. On 

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

 pentadactyle Vertebrata, the hyoid takes no share in 



Br.l 



Fig. 137. Head of Embryo Dogfish (11 lines long). 



TT, Trabecula ; fl, Pt, jiterygo-quadrate ; m Ft, rneta- 

 pterygoid ; Mn, mandibular cartilage ; ay, hyoid arch ; 

 Br 1, first branchial arch, with Jour succeeding 

 arches; sp, mandiimloliyoid cleft; cl, hyo-branchial 

 cleft; ci,c2,c3, cerebral vesicles. (After Parker.) 



