128 



LECTURE V. 



There are neither pectoral nor ventral fins in the Cyclostomous 

 Fishes. In the Plagiostomes there are both : but the scapular arch is 

 detached from the occiput, the condition of its displacement being 

 the more posterior position of the heart in these fishes. In the Sharks 

 and Chimaeras it is loosely suspended by ligaments from the vertebral 

 column : in the Rays the point of resistance of their enormous 

 pectoral fins has a firmer, but somewhat anomalous attachment, by the 

 medium of the coalesced upper ends of the supra-scapular pieces to 

 the summits of the spines of the confluent anterior portion of the 

 thoracic abdominal vertebrae. In the Sharks the scapular arch con- 

 sists chiefly of the coracoid portions {^fig. 42. 52), which are confluent 

 together beneath the pericardium which they support and defend; 

 the scapular ends of the arch, connected to the coracoids by ligament, 

 project freely upwards, backwards, and outwards. To a posterior 

 prominence of the coracoid cartilage corresponding with the anchy- 

 losed radius and ulna {ih. 54, 55) in the Lophius, there are attached, 

 in the Dog-fish and most other Sharks, three sub-compressed, sub- 

 elongated carpal cartilages, the uppermost {ib. 56) the smallest, and 

 styliform ; it supports the upper or outer phalangeal ray. The 

 next bone {ih. 56') is the largest and triangular, attached by its 

 apex to the arch, and supporting by its base the majority of the 

 phalanges. 



Cartilages of the pectoral fin and arch of the Dog-fish (Spinax acanlhias). 



The third carpal {ih. 56'') is a smaller but triangular cartilage, and 

 supports six of the lower or radial phalanges. Three joints (meta- 

 carpal and digital) complete each cartilaginous ray or representative 

 of the finger {ih. 57) ; and into the outer surface of the last are in- 

 serted the fine horny rays or filaments {ib. 57"), the homologues of 



