OF THE SKULL IN SHARKS AND SKATES. 231 



ostean fishes ; but in the Eel {Anguilla acutirostris) and its congeners there is a less 

 degree of specialization of the Eaiine type of face. 



In small, ivhite young of that species, 2-| inches in length (the gift of Mr. F. Buck- 

 land; see ' Nature,' June 22, 1871, pp. 146-148), I find the following modifications of 

 the Teleostean face. 



The hyomandibular has a most extensive otic region, the front and hinder head 

 being far apart, and under the latter the opercular knob. This transverse top grows 

 downwards, as an arcuate rod, with its convexity behind. 



It is ossified by the hyomandibular centre down to the bent part ; then there is a 

 large tract of cartilage, which has its pointed forward end capped by a syraplectic bony 

 sheath, which passes inside the quadrate in front of it. 



On the back of the middle of the synchondrosial tract there is an interhyal nucleus 

 of cartilage, from which a ligament grows ; and to this ligament the hyoid cornu is 

 suspended. This cornu does not separate off" into a hypohyal below; and the epi- 

 and ceratohyals completely ossify the rod, largely overlapping each other. 



Below its front condyle the hyomandibular sends forwards and downwards two strong 

 sharp spines of periosteal bone ; and these embrace the ascending but lowered head of 

 of the mandibular suspensorium, which is a shortish straight rod, unossified above and 

 below. 



Its ossification is a cylindrical, ectosteal quadrate ; and the apex receives no meta- 

 pterygoid bony centre. ' 



As in the Urodeles, there are a bony and a cartilaginous pterygoid ; the former is a 

 delicate f-shaped style, pedate behind, to run up the front face of the suspensorium. 



The cartilaginous pterygoid {r.pg, rudiment of pterygoid) is a triangular process, 

 growing from the front of the quadrate bar below, exactly as in the larva of every known 

 kind of Caducibranchiate Urodele, as well as in certain Perennibranchiates ; it is also the 

 arrested homologue of the part which, in the Salmon, coalesces with the ethmopalatine, 

 and also of the extended limb of the " upper jaw " of the Selachian. 



The ethmopalatine is suppressed in the Eel, and its skull is as simple as that of a 

 Snake or of the Proteus. 



But a skull whose structure has long puzzled me, namely that of the Siluroid Clarias 

 capensis, comes in as the most demonstrative proof of the existence of a prseoral post- 

 nasal visceral arch. 



As in the Eel and its congeners, the hyomandibular of Clarias has an extensive otic 

 region ; and, as in the Eel, the fore part of that bone develops an extraordinary amount 

 of periosteal bone in front, which aborts, or coalesces with the metapterygoid. 



The whole pterygo-quadrate arcade is a broad, flat, almost transverse plate, not ascend- 

 ing behind into an otic process, but being angular behind and above the quadrate con- 

 dyle, and strongly wedged in between the foregrowths of the hyomandibular and the 

 separate symplectic bone. 



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