288 MR. W. K. PARKER ON THE OSTEOLOGY OF BAL^NICEPS REX. 



it represents the "conjoined bases of the orbito-sphenoids in mammals:" we quite 

 coincide with Dr. Hallman and Professor Huxley that its supposed representative in 

 the Carp is the orbito-sphenoid ; but not with Agassiz (with whom Professor Owen once 

 agreed in this matter) that it is a cranial ethmoid. It does not agree with that hinder 

 part of the connate orbito-sphenoids in the Carp which props up, and therefore lies 

 beloic as well as in front of the ali-sphenoids (see Professor Huxley's figure of the section 

 of the Carp's skull, Croon. Lect. p. 24)'. This is not really a digression (for the crania 

 of the Vertebrata mutually explain each other) ; we will therefore give one word more 

 about this elegant little bone. In the Sea-bream {Pagellus centro'dontus) the structure 

 of a typical fish can be well seen. Looking at the floor of this creature's skull, three 

 remarkable bridges of bone are seen along the medial line : the hindermost of these is 

 formed by the meeting of the ex-occipitals above their centrum ; the middle bridge is 

 formed in the same way by the petrosals, the basi-sphenoid lying at a great distance 

 below the cranial floor ; whilst the first bridge is formed by a single bone (this ' ento- 

 sphenoid '), as though it were the serial homologue of these two pairs of bones behind. 

 If this most anterior bridge belong to the same category as the petrosals and lateral 

 occipitals, it should not directly precede the former were it the orbito-sphenoid ; and it 

 is not a lateral element ; for perched up above and between it and the petrosals are the 

 ali-sphenoids — pretty constant in fishes, but always high up, being feeble ossifications 

 of the antero-lateral parts of the primordial skull, and lying in the midst of the still 

 unossified cartilage that projects forwards on each side from the boundary of the great 

 fontanelle. In the Reptilia proper the orbito-sphenoid is seldom present as a distinct 

 bone ; for, although the roof-bones of the pre-sphenoidal sclerotome are largely developed 

 as the ' principal frontals,' the neurapophyses and centrum are arrested. In the Batra- 

 chia they break out again, the neurapophyses forming the ring, and the centrum (pre- 

 sphenoid) the septum, of the ' os en ceinture ' (see Goodsir, op. cit. p. 157). 



Pre-sphenoid. (PI. LXV. fig. 1 , psp & eth.) 

 The pre-sphenoid of the Balaeniceps is large and well-developed : no part of it can 

 be seen from above, the roof-bones being very perfect ; but it projects a line or so in 

 front of them, just touching its serial homologue the ethmoid. All trace of the union 

 of the orbital processes of the sphenoido-frontals with the pre-sphenoid is lost ; but 

 the groove for the olfactory nerve, and a descending process on each side marking 

 the limits of the nasal fossae (which are continued backwards for four lines on each side 

 of the pre-sphenoid at its upper part) show where we are. This descending process is 

 just behind the ' hinge,' half an inch mesiad of the orbital margin. A strong fascia 

 connects it with another smaller projection on the side of the thick carinate anterior 

 part of the pre-sphenoid, half an inch below the widely-dilated part which props up the 



The so-called 'ento-sphenoid' is properly an ' orbito-pre-sphenoid' in such fishes as the Carp and Salmon ; 

 but we class the httle Y-shaped bone of the Percoids with the 'rostrum' of birds and the higher reptiles. 



