NOTIDANI 



139 



attachment of the jaws is more or less amphistylic, the branchial 

 slits are six or seven in number, and there is only one dorsal fin, 

 In the second group, the jaws are attached in modern forms on the 



<ia 



af. f pef 



Fig. OS. 



Diagram of the branchial circulation of an Elasmobranch fish (modified from T..J. Parker), 

 a. a, median anterior prolongation of aorta; re.c, anterior carotid, efferent vessel of spiracular 

 gill (pseudobranch) ; a.ef, efferent vessel from last hemibraneh; re./, anterior efferent vessel; 

 aj -•>', live afferent vessels from ventral aorta ; af.a, afferent artery of spiracular gill ; c, conu.s 

 leading to ventral aorta ; • ', coeiiac artery ; d, dm fci»a Gti\ ieri ; d.a, dorsal aorta ; ef, epi branchial 

 artery; h.a, liyoid efferent vessel ; hp, hepatic veins; lit, heart; p.t, posterior carotid; p.rf, 

 posterior efferent vessel ; ~, spiracle : v.a, ventral artery ; I-V, branchial slits. 



hyostylic plan, there are not more than five branchial slits (with one 

 exception, p. 152), and there are two dorsal fins (Miiller u. Henle 



Fig. 99. 



Diagram showing the principal modifications in the arrangement of the hyoid arch in the 

 Selachii. (After Gegenbaur, from Sedgwick's Zoology.) A, in Heptanchus ; B, in a shark; 

 C, in Torpedo; D, in Raja. Jim, hyomandibular ; hy, lower part of hyoid arch; p, process 

 supporting .jaw-articulation ; r, branchial rays. 



[308], A. S. Woodward [505], Dunienl [124], Regan [346], Jaekel 

 [238], etc.). 



Group I. 

 Sub-Order 1. NOTIDANI. 



These sharks have a skull and jaw apparatus built on the 

 amphistylic plan. In Heptanchus, the palato-quadrate is firmly 



