68 



LECTURE III. 



anal fins, depend on the development and grouping of the accessary 

 and intercalary spines : the true vertebral, neural, and htcmal spines 

 give scarcely more indication of the nature or existence of those fins, 

 than the neural spines in the Porpoise or Fin-whales do of their not 

 less essentially though more histologically dermal dorsal fin ; but the 

 development of the dermo-skeleton, in the fish's fin, and its inter- 

 calation with the spines of the endo-skeleton, and consequently its 

 retention in our prepared skeletons, lead me to notice it in connection 

 with the vertebral column, as I shall subsequently, for similar reasons, 

 have to describe parts of the dermo-skeleton which are intercalated 

 with, or appended to, the vertebras and bony arches of the head. 



In the Dermopteri (Lampreys, Lancelet), the dorsal, anal and 

 caudal fins are simply cutaneous folds, with scarcely distinguishable soft 

 fibres for rays, and they are continuous, as in the embryos of higher 

 fish. In the Gymnotus, a very long but shallow anal is continued 

 into the caudal fin ; but, as the name of this fish implies*, there is 

 no dorsal fin. In many, both cartilaginous and osseous fishes, a single 

 group of dermal spines supports a single dorsal fin, as in the Sturgeon, 

 the Grey Shark {TIeptanchus), and the Shad : in others, as the Dog- 

 fish ( Sjiinax), and the Mullet, there are two groups of dermo-neural 

 spines and two dorsal fins ; in the Cod and its congeners there are 

 three dorsals {fig. 19. d) ; in the Pohjpterus there az*e, as its name 

 implies, numerous (as many as sixteen) dorsal fins ; and many ac- 

 cessary vertical finlets, both dorsal and anal, may be seen in the 

 Caranx, or Mailed Mackerel. 



Cuvier called those bony fishes " Malacopterygian," whose verti- 

 cal fins were supported by soft, jointed, and branched dermal spines, 

 and he called those " Acanthopterygian," which had the fin-rays or 

 some of the anterior ones in the form of simple, unjointed, and un- 

 branched bony spines : but we have seen that these variable parts of 

 the dermo-skeleton form unsafe and artificial grounds for the larger 

 groups of the class. 



Very rarely do the interneural and dermal spines coincide in 

 number with the neural spines : they are often more numerous, as in 

 Acanthurus and Pleuronectes ; more frequently less numerous, as in 

 the Lepidosteus or Trachinus. The Lophius has only three long de- 

 tached dei*mal rays, projecting from above the abdominal region of 

 the spine, and two or three above the cranial vertebra; ; the base of 

 these dermal spines expands, bifurcates, and the extremities curve 

 inwards, to be inserted into lateral depressions, or a transverse per- 

 foration, of the summit of the interneural spine, represented in 

 Lophius by a small semi-osseous disc. Those dermal spines that 

 sustain the caudal fin offer the lowest condition, as might be expected 



* Gr, yvp.vos, naked ; votos, back. 



