86 STUDIES ON THE ELASMOBRANCH SKELETON, 



entrance is situated nearly directly behind the articular surface 

 about the middle of the arch ; from this two canals lead, the one 

 short and wide, passing outwards and a little forwards and 

 downwards to open on the outer surface, the other narrow, and 

 passing upwards, forwards, and slightly outwards to end above and 

 behind the articular surface on the inner aspect of the cartilage 

 close to the anterior border. The upper canal described by 

 Gegenbaur in Scyllium, Oaleus and Pristiurus is indicated on the 

 right side only by a slight depression. 



The Pectoral Fins. (Plate I., fig. 3.) 



As in Carcharias,* the pro- meso- and meta-pterygia are all 

 well developed and the latter is greatly elongated, having a large 

 number of rays articulating with its pre-axiad border ; but the 

 mesopterygium is mt quite distinct from the metapterygiuui, in fact 

 is completely coalescent with it at the base, whereas in Carcharias 

 the two cartilages remain cpiite separate. Articulating with the 

 distal extremity of the propterygium is a lateral cartilage, formed, 

 as in Scyllium, Pristiurus and Carcharias by the coalescence of the 

 bases of three posterior propterygial rays, but not continuous with 

 the latter — being separated from them by an articulation or 

 interval of fibrous tissue ; the front ray, which is very short, 

 remains distinct and articulates separately with the propterygiuni. 

 The propterygium and mesopterygium are relatively more important 

 than in Carcharias, nine rays in all articulating with them ; the 

 bases of the last four mesopterygial rays are coalescent for a short 

 distance. The elongated metapterygiuui articulates at its distal 

 extremity with two accessory cartilages, the posterior of which is 

 much the longer and bears nine rays, while the anterior bears 

 three. The bases of four of the rays which articulate with the 

 metapterygium are coalescent in pairs for a short distance at the 

 base. 



The arrangement of the basal cartilages described above seems 

 to place the pectoral fin of Carcharodon in an intermediate position 



* Gegenbaur, " Untersuehunger zur vergleiehenUen Anatomie der Wirbelthiere." Heft, 

 2, 2te. Abschnitt, Brustflosse der Fische, p. 142, Tab. IX., fig. 5 (1365.) 



