OF THE PAIRED FINS OF EI.ASMOBRANCHS. 



59 



Before dealing with the development of the skeleton of 

 the fin, it will be convenient to describe with great brevity 

 the structure of the pectoral and pelvic fins of the adult. 

 The pectoral fins consist of broad plates inserted horizontally 

 on the sides of the body ; so that in each there may be dis- 

 tinguished a dorsal and a ventral surface, and an anterior 

 and a posterior border. Their shape may best be gathered 

 from the woodcut (fig. 1) ; and it is to be especially noted 



Tig. 1. 



Pectoral fins and girdle of an adult of Scyllhim canicula 



(natural size, seen from behind and above.) 



CO. Coracoid ; sc. scapula; pp. propterygium ; me p. mesopterygium ; 



mp. metapterygium ; fn. part of fin supported by horny fibre. 



Fig. 2. 



Right pelvic fin and part of pelvic girdle of an adult female of Scyllium 

 canicula (natural size). 



il. Iliac process ; pn. pubic process, cut across below ; hp. basipterygium ; 

 af. anterior cartilaginous fin-ray articulated to pelvic girdle ; fn. part of fin 

 supported by horny fibres. 



that the narrowest part of the fin is the base, where it is 

 attached to the side of the body. The cartilaginous skeleton 



