FINS OP O-AlfOIDS AND TELEOSTS. 579 



modified and Highly specialized spiaes have apparently fused 

 together to form a curious boat-like structure furnished with 

 two large lateral foramina, through which are transmitted the 

 depressor muscles of the first spine and the erectores of the 

 second. Anteriorly this singular fin-support rests on the 

 posterior face of the skull, and behind in is attached by ligament 

 to the distal end of a fairly stout, shaft-like bone, the " tige 

 apophysaire" of Holland*, the proximal extremity of which is 

 in ligamentous connexion with the distal end of one of the 

 anterior neural spines. The identification of the component 

 elements of the fiu-support is extremely difiicult in adult speci- 

 mens, and hence any comparison with the more normal elements 

 of the posterior dorsal fin is likely to prove misleading. I am 

 inclined to think that three radial elements enter into its 

 formation, bub to what extent the usual segments of these 

 elements are represented I can oS"er no opinion. 



Posterior Dorsal fin. — In this fin there are twenty-seven radial 

 elements, supporting a corresponding number of soft, branched 

 and multiarticulate fin-rays. All the radial elements (PI. XXIIT. 

 fig. 34, r.e.) are bi^egmental, each consisting of a proximal (p.s.) 

 and a distal (d.s.) segment. The proximal segments exhibit a 

 general resemblance to the ordinary dagger-shaped bones of other 

 Teleosts, and for the greater part of the length of their parallel 

 and serrated anterior and posterior margins are in close sutural 

 connexion with one another, the union in those more posterior 

 extending even to partial anchylosis ; they also interdigitate 

 with the subjacent neural spines, to which they are firmly and 

 rigidly attached. Superiorly, the proximal segments terminate 

 in cartilaginous extremities, which are in close apposition and 

 form an even dorsal margin traversed by a slight longitudinal 

 groove for articulation with the series of distal segments. On 

 the outer surface of each proximal segment there is a prominent 

 longitudinal bony ridge, which, however, ceases a little short of 

 the extreme distal end of the segment. 



The distal segments, on the contrary, are small, somewhat 

 cubical, cartilaginous nodules with flat distal and convex 

 proximal surfaces, and so arranged that while in close ligamen- 

 tous connexion with one another in a longitudinal series they 

 tend to alternate with the proximal segments. The connexion 



* Quoted by Sorensen, I. c, 



46* 



