134 LECTURE VI. 



are no separate liomologues in the Sturgeon's fin of the bones called 

 ulna and radius in Osseous Fishes : the carpal bones {ib. 56) imme- 

 diately articulate with the coracoid, and support about thirty rays 

 {ib. 57), two or three of which seem to have coalesced to form the 

 strong bony spine {ib. 51') on the outer border of the fin. 



The ventral fins are small and are suspended each by a simple 

 cartilaginous pubis to the abdominal muscles a little in advance of 

 the anus. 



The osseous scales on the upper surface of the skull are so ar- 

 ranged as, at first sight, to suggest certain analogies with the epi- 

 cranial bones. Thus, the scale marked a {ib. d 3) in Brandt and 

 Ratzeburgh's figure of the head of the Accijienser Sturio* might 

 be compared with the supra-occipital bone ; the pair in advance 

 {ib. d 7), marked e (loc. cit.), with the parietals ; and the pair {d 11) 

 marked g (loc. cit.), with the frontals ; but then these are sepa- 

 rated by an interfrontal osseous plate, and in Accipenser Scypha by 

 two or three such plates ; the supra-occipital plate is divided in the 

 A. brevirostris and in the A. sturio of Pallas f, and other varieties 

 occur which render the attempt to illustrate the homology of the 

 true epicranial bones in Osseous Fishes by these dermal ganoid plates 

 in the Sturgeons difficult and unsatisfactory. The median plates are 

 more obviously and essentially a continuation forwards of the dermal 

 spinous plates {ib. ds), from the mid-line of the back ; and we may 

 see their more veritable repetition amongst the Osseous Fishes in the 

 dermal epicranial spines, for example, of the Angler {Lophius), which 

 support the long fishing filaments upon the head, or in those modified 

 ones forming the sucking disk on the head of the Remora. They are 

 more obviously homologous with the dermal bones forming the helmet 

 of the Armadillo, and bear the same relation in the Sturgeon to the 

 cartilaginous skull as those bones do in the Armadillo to the osseous 

 skull beneath. 



The lateral series of dermal bony plates {ih. dp) are also con- 

 tinued upon the head, and seem to represent in the Sturgeons the 

 supra-scapular {ib. d 5o) and the opercular bones {d 35) in osseous 

 Fishes. Other constant sei'ies of cranial scale-bones, in the Sturgeon, 

 circumscribe the orbits below and the temporal spaces above. But 

 before applying the well-contrasted states of the endo- and exo- 

 skeleton of the Sturgeon to the determination of the bones of the 

 skull in the Cod, I may advert to the reversed conditions of the endo- 

 and exo-skeletons in the Lepidosiren, which lends another valuable 

 aid in the solution of this difiicult and much discussed subject. The 



* Medizin Zoologie, l)and ii. tab. iii. f Fauna Rosso- Asiatica, iii. p 91. 



