MR. W. K. PARKER ON THE OSTEOLOGY OF BALyENICEPS REX. 287 



larger, which is continued as an open groove forwards and a little upwards into the 

 nasal fossa. This groove is on the side of the upper thick part of the pre-sphenoid : 

 the foramen itself, although single, answers to the many foramina of the cribriform 

 plate of the ethmoid in mammals in function (for it carries the olfactory nerve), but not 

 actually, seeing that the ethmoid of birds is facial and not cranial. The recess in 

 which the ' rhinencephala ' lie is formed by the diverging plates of the connate orbito- 

 sphenoids below and by the frontals above ; and although these lobes are the most 

 anterior part of the brain, they are pitched up, as it were, against the roof-bones. 

 The optic foramina mark the point where the orbito-sphenoid has become single and 

 passes downwards and forwards, losing itself in front in the pre-sphenoid, and becoming 

 confluent below with the 'rostrum' of the basi-sphenoid. 



A fossa above the optic foramen is the upper landmark of the connate orbito- and 

 pre-sphenoids — the neurapophyses and centrum of this semi-catacentric sclerotome, so 

 curiously modified in relation to the large eye-balls. The centre of the originally 

 membranous wall between the orbits is unusually well developed in Balaeniceps, being 

 generally arrested more or less in the Bird-class ; it is, however, in this bird all 

 converted into bone, the diploe of which is scarcely absent from even the central part. 

 Although, for convenience-sake, we have separated the orbito-sphenoid from the pre- 

 sphenoid in description, they are nevertheless only parts of one large inter-orbital 

 ossification in the class of Birds. 



The thick anterior part of the pre-sphenoid is the first to ossify ; this process com- 

 mencing in the Chicken about the twelfth day of incubation, and in the Pigeon near the 

 time of hatching. The latter bird is able to fly before any of the orbito-sphenoidal 

 region is ossified ; and both the Chicken and the Emeu have attained a considerable size 

 before the ossific matter reaches the ali-sphenoids. 



In such birds as the Rail and Water-hen, the Grebe and the Cormorant, the interor- 

 bital septum is very incomplete. The leg of the inverted Y-shaped process bounding 

 the common optic passage in Gallinula chloropus is an exogenous spur growing back- 

 wards and downwards from the pre-sphenoid ; but nearly at right angles with this, 

 another spur projects forwards and downwards. This latter spur, with the diverging 

 alse that coalesce with the ali-sphenoids just above each optic foramen, might easily 

 be mistaken for the actual representative of the little Y-shaped interorbital bone of 

 such fish as the Perch and the Sea-bream {Pagellus centrodontus) . This latter ossicle 

 has indeed been a ' bone of contention : ' it is the ' sphenoide anterieur ' of Cuvier, the 

 ' entosphenal ' of GeofFroy, the ' os innominatum ' of Hallman, and the ' ethmoide 

 cranien ' of Agassiz ; whilst Professor Owen, calling it the ' ento-sphenoid,' considers it 

 to be the internal part of the centrum of the pre-sphenoidal vertebra ; but its real 

 nature was well seen by Professor Goodsir, who considers it to be a feebly developed 

 centrum of the post-sphenoid, or perhaps even of the temporal sclerotome. We do not 

 agree with Cuvier that it is part of the anterior sphenoid, nor with Professor Owen that 



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