OF THE LAEVAL POLYPTEEUS. 323 



The stylohyal (PI. XXXIII. figs. I, 2, St.IIy.) is a rounded mass of cartilage wliich 

 takes no part in the suspension of the jaws. 



The ceratohyal (PI. XXXIII. figs. 1, 2, 3, C.Hy.) is massive at either end, but 

 constricted to a narrow bar in its middle portion. 



The hypohyal (PL XXXIII. figs. 1,2, 3, HJIy.) is an almost spherical cartilage 

 connecting the front end of the ceratohyal with that of the 1st branchial bar. 



The hasibranchial (PI. XXXIII. figs. 2, 8, B.Br.) is a massive median cartilage on 

 either side of which are articulated the enlarged lower ends of the four branchial bars. 

 Each of these bars, in passing backwards and upwards, becomes very slender. 

 Posteriorly these become slightly thickened again and curve inwards ; finally the 

 upper end of the first branchial abuts upon the cranial wall just below the articalation 

 of the hyomandibular, while the 2nd, 3rd, and 4th branchials tapering, curve 

 downwards and end freely close under the auditory capsule (PI. XXXIII. 

 figs. 1, 2, 3, Br. 1, 2, 3, & 4). 



Between the palatoquadrate and mandibular cartilage there lies a crescent-shaped 

 labial cartilage with its convex surface forwards, the upper horn being more slender 

 than the lower (PL XXXIII. figs. 1, 3, Lb.). 



In the arrangement of the cartilages of the suspensorial apparatus the larval 

 Folypterus exhibits a condition exactly intermediate between that of the hyostylic 

 Selachians and the Teleostei, there being no very intimate union between the palato- 

 quadrate and hyomandibular cartilage by means of a symplectic cartilage corresponding 

 to that of Teleostei. The general correspondence of the arrangement with that of the 

 larval Salmon on the one hand and the hyostylic Selachii on the other, and 

 the relation of the spiracle to the hyomandibular in Polypterus, seem to me to go 

 a long way towards dispelling doubts as to the homology of the suspensorium of the 

 Teleostei with that of the hyostylic Selachii, such as have been entertained by some 

 authors ^. In this particular of course Polypterus diff'ers widely from all living 

 Amphibia, where the palatoquadrate bar has become fused with the cranial wall and 

 the hyomandibular usually reduced. 



On the other hand, the presence on the hyomandibular of Polypterus of a segmented 

 rod of cartilage supporting the external gill is paralleled in the Aistopodous 

 Stegocephali ; for in BoUchosoma longissimum, according to Fritsch -, there is found 

 attached to the hyoid arch a skeletal structure which apparently supported an external 

 gill. It is difficult, however, to make out whether this structure was attached to 

 the periotic portion of the skull itself or to the upper end of the hyoid arch. 



' See H. B. Pollard, " The Suspension of the Jaws in Eish," Anatomisohe Anzeiger, x. p. 17. Also Parker 

 and Haswell, ' Text-book of Zoology,' vol. li. p. 202. 



^ Fauna der Gaskohle und der Kalksteine dor Permformation Bohmens. 



VOL. XVI. — PAUT VII. No. 2. — October, 1902. 3 a 



