TIIK SKULL OF OSSEOUS FISHES. 129 



the claws and nails of higher Vertebrata, but which on their first ap- 

 pearance, in the present highly organised class of fishes, manifest, 

 like other newly introduced organs, the principle of vegetative repe- 

 tition, there being three or four horny filaments to eacli cartilaginous 

 ungual phalanx. 



On the fore part of the coracoid arch, near to the prominence sup- 

 porting the fin, there are developed a vertical series of small bony 

 cylindrical nuclei in the substance of the cartilage in most Sharks. 

 In the Rays the coraco-scapular arch forms an entire circle or girdle 

 attached to the dorsal spines : it consists of one continuous cartilage 

 in the Rhinohates, but in other Rays is divided into coracoid, scapular, 

 and suprascapular portions, the latter united together by ligament. The 

 scapula and coracoid expand at their outer ends, where they join each 

 other by three points, to each of Avhich a cartilage is articulated homo- 

 logous with the three above described in the Shark, and which imme- 

 diately sustain the fin-rays. The posterior cartilage answering to 

 the upper one in the Shark curves backwards and reaches the ventral 

 fin : the anterior cartilage curves forwards, and its extremity is joined 

 by the ant-oi'bital process as it proceeds to be attached to the end of 

 the rostral cartilage ; the middle proximal cartilage is comparatively 

 short and crescentic, and sustains about a sixth part of the fin-rays, 

 which are the longest, the rest being supported by the anterior and 

 posterior carpals, and gradually diminishing in length as they ap- 

 proach the extremities of those cartilages. In the common Ray there 

 arc upAvards of a hundred metacarpo-phalangeal rays in each great 

 pectoral fin. The longest rays begin after the tenth or eleventh joint 

 to bifurcate ; the shorter ones bifurcate progressively nearer their 

 origin. 



The venti-al fin is better developed in the Plagiostomes than in 

 any other fishes. The supporting arch consists indeed of the same 

 simple pubic elements, united together by ligament in the middle 

 line, and loosely suspended in the abdominal walls, but ihey do not 

 immediately support the fin-rays. Two intermediate cartilages qre 

 articulated to the expanded outer end of each pubis ; the anterior is 

 the shortest in the Dog-fish, and supports three or four rays ; the pos- 

 terior one is much longer, and supports the remainder of the rays, 

 fifteen or sixteen in number. To the end of this cartilage likewise 

 is attached, in the male I'lagiostomes and Chim;era^, the peculiar ac- 

 cessary generative organ or clasper. 



In the Torpedo the pubic arch sends forwai'ds two processes like 

 marsupial bones ; these processes are longer in an extinct Ray to 

 which its discoverer Sir P. de M. Grey Egerton has given the name 

 of Cyclohates oligodactylus (xL. p. 225. pi. 5.). 



VOL. }I. K 



