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



the pre-maxillaries are fused together, and the evanescent frontal process on which they 

 were modelled has begun to shrink. 



That the ' rostrum ' of the Chelonians and Crocodiles is an unsymmetrical mesial 

 ossification we have no doubt ; not so the lower part of the so-called basi-sphenoid, 

 Rathke says (Croon. Lect. p. GO) that " the body of the basi-sphenoid is (in the Snake) 

 formed between the posterior fontanelle of the basis cranii and the pituitary space, 

 therefore far from the cephalic part of the chorda ! It ossifies by two lateral centres, 

 each of which forms a ring round the carotid canal." This is exactly what occurs in 

 the Chick ; and we find that in the Chameleon (where the rostrum is feebly developed) 

 these basi-temporal centres retain the posterior half of their connecting suture, whilst 

 a trace of it still remains in the adult Blind-worm' {Anguis fragilis) . 



In young specimens of the Crocodilus acutus from San Domingo (for which we are 

 indebted to Henry Power, Esq.), we find that the rostrum had coalesced with the basi- 

 temporals, and these with each other, leaving a large open space between the tables of 

 bone ; and yet these specimens were only recently hatched when taken, the abdomen 

 being nearly full of unused yolk-substance. 



In the Pigeon, one day after hatching, the two halves of this lower piece, which 

 Professor Goodsir would call the temporal centrum, had coalesced ; but in large 

 ' squabs ' a week old, this underlapping piece was easily separable from the upper piece 

 or true basi-sphenoid. 



Nothing that we have ever seen in anatomical structure is more elegant than the 

 condition of these parts in the Balaeniceps and the Heron ; in the latter they are essen- 

 tially a miniature of those of the former : this is certainly not a faint and superficial 

 mark of afiinity. 



That cranial centra may be developed from a pair of lateral centres is seen in the 

 morphology of the human sphenoid bone (Meckel, as quoted by Professor Owen, Report on 

 Archetype, p. 318), in the double ethmoid and vomer of the great Sudis {Arapaima gigas), 

 and in the condition of the vomer and turbinals of the Lacertian and Ophidian, — the 

 former (the vomer) being evidently a pair of latero-basal ossifications of the ethmoid, 

 and the turbinals the corresponding pterapophyses or outgrowths of the ethmoidal 

 sclerotome. 



Basi-sphenoid. (PI. LXV. figs. 1 & 7, & s.) 

 Many birds have, like the Mammalia, two pairs of basi-sphenoidal pterapophyses, an 

 inner pair abutting against a process from the pterygoid (its proper cranial attachment), 



' Since the above was written, we have dissected a young specimen of Emys europcea, and find that the basi- 

 sphenoid is developed from a pair of lateral inferior centres, which soon coalesce in front, and then send forwards 

 a triangular wedge of bone to fit-in between the pterygoids. In this specimen the ' rostrum,' which is the 

 homologue of the basi-sphenoid of the Bird, is a knife-like plate of cartilage, which never ossifies in this and 

 other small Chelonia. In the Crocodiles, in the Green Turtle, and in the ' Loggerhead ' it does ossify. 



