120 THE VERTEBRATE SKELETON. 



The visceral arches of Elasmobranchs may be summa- 

 rised as follows : 



1. The mandibular arch, consisting of a much reduced 

 dorsal portion, the pre-spiracular ligament, and a greatly de- 

 veloped ventral portion from which both upper and lower 

 jaws are derived. The mandible (Meckel's cartilage) is the 

 original lower member of the mandibular arch, and from it 

 arises an outgrowth which forms the upper jaw or palato- 

 pterygo-quadrate bar. In Scymnus this bears a few branchio- 

 stegal rays. 



2. The hyoid arch, which consists of the hyomandibular 

 and the hyoid, and bears branchiostegal rays on its posterior 

 face. 



3. The branchial arches, generally five in number, all 

 of which except the last bear branchiostegal rays. In the 

 Notidanidae the Dumber of branchial arches is increased 



FIG. 17. DORSAL VIEW OF THE BRANCHIAL ARCHES OF 



Heptanchus. (From GEGENBAUR). 



1. basi-hyal. 7. pharyiigo-branchial, common 



2. cerato-hyal. to the sixth and seventh 



3. second hypo -branchial. arches. 



4. first cerato-branchial. 8. basi-branchial of second arch. 



5. first epi-branchial. 9. basi-branchial, common to the 



6. first pharyngo-branchial. sixth and seventh arches. 



