414 "• B. POLLARD, 



The Cranium and other Parts. 



Coucerning the skull it is not my iutentiou to enter into any 

 great amount of detail. A cartilaginous tegmeu cranii is not formed. 

 However across the great fontanelle runs the epiphysial bar, beneath 

 and slightly in front of which the pineal organ terminates. It divides 

 the fontanelle into an anterior and posterior portion and the anterior 

 part corresponds to the Selachian "Praefrontalliicke" (Gegenbaur) in- 

 asmuch as a prolongation of the pineal organ is said to terminate 

 at the anterior border of the tegmeu cranii. Parkeu has described 

 the tegmeu cranii in the Salmon. An epiphysial bar is shown by 

 Sagemehl in Characinidae and Cyprinidae. It is represented by a 

 rudimentary block of cartilage, discovered by myself in Poly2>terus, 

 and Gaupp has followed its development in the tadpole, terming it 

 the Taenia tecti transversalis. The main fontanelle in the frog thus 

 corresponds to the Praefrontalliicke of Selachii. It is interesting to 

 note that the cartilage follows the wandering of the pineal organ 

 backwards, but the dermal bones do not, the pineal organ shifting 

 from between the frontals to between the parietals. 



There is considerable variation in the floor of the brain, cartilages 

 remaining only as blocks or processes, paired or unpaired. 



A preorbital process is not formed in Trichomycterus , but by 

 various degrees it reaches a complete development as in Silurus. 



One of the most remarkable features is the Rostrum or modifi- 

 cation of the internasal septum. It is most marked in Trichomycterus 

 and Auchenaspis. It becomes invaded by the so called dermethmoid 

 bone. We have only to consider the rostrum somewhat prolonged to 

 obtain a typical Sturgeon rostrum. The Sturgeons cannot be very far 

 removed from the Siluroids, more especially the Hypostomidae , as 

 indeed is suggested by Huxley's observations on the relation of the 

 fossil forms. 



The comparative anatomy of the hyomandibular is of very great 

 interest, but, since I have already dealt with the subject in a paper 

 on the suspension of the jaws, I need not refer to it in detail here. 

 The hyomandibular articulates with the pterotic ridge by a long 

 articulation. The immobility of the Suspensorium of Hypostomidae is 

 well known. 



In Glorias the pterotic ridge is produced far outwards, the arti- 

 culation of the hyomandibular lying some way from the cranial wall. 



