MR. W. K. PARKER ON THE OSTEOLOGY OF BAL^NICEPS REX. 277 



process is, according to Owen, formed in the Emeu by a distinct ossific centre'. We 

 possess a sketch of it, from a dissection made by us many years ago of an Emeu only 

 six weeks old. 



This exceptional ossific centre appears to be the actual representative of the post- 

 frontal of the cold-blooded vertebrates, and to be the upper neurapophysis of the pre- 

 sphenoidal sclerotome. Professor Goodsir places it to the account of the post-sphenoid, 

 the roof-bones of which, he says, are deficient in all the Ovipara^. In many birds, e. g. 

 Parrots, Gallinae, and the Adjutant, &c., the lower part of the temporal fossa is bridged 

 over in front by the union of the post-frontal with a sort of zygomatic process of the 

 squamosal. 



In Balaeniceps, the Heron, and the Boat-bill, the spur of the squamosal is quite rudi- 

 mentary. 



Professor Goodsir {loc. cit.) considers that the so-called ' frontals ' of the Ovipara are 

 not the homologues of the Mammalian frontals ; these latter bones, besides roofing-in 

 the ethmoidal region of the Mammal (which in that class is included in the cranium), 

 contribute largely to the formation of the great cranial dome. The homologues of these 

 latter bones are, according to him, to be found in the so-called ' nasals ' of the Bird and 

 prefrontals of the Reptile ; but this requires much renewed investigation. The upper 

 .surface, therefore, of the Bird's skull is formed in front by sphenoido-frontals, and behind 

 by the parietals. In Mammalia, the temporo- or inter-parietal, as a rule, is single'; 

 but in the Muridse, and in the Common Mole, this piece is relatively as large as both 

 the parietals in many of the Ovipara. In the latter animal the proper frontals, called 

 ethmoido-frontals by Goodsir, are very little extended beyond the ethmoidal region. 



Squamosal (Pi. LXV. figs. 1, 3, G, & 7, sq). — The element to which the ' quadratum ' 

 is suspended Cuvier calls 'temporal' in birds, and 'mastoid' in reptiles and fishes; 

 Agassiz calls it ' ecaille du temporal'; and Professor Owen considers it to be the 

 ' mastoid' in all the Ovipara. Dr. Hallman calls it ' squama temporis'; and we quite 

 agree with Professor Huxley when he says (speaking of it in the bird), " there is not a 

 single relation (save the connexion with the jugal) in which this bone does not resemble 

 the squamosal of the Mammalia ; there is not one in which it does not differ from the 

 mastoid" (Croon. Lect. p. 14). 



In the Chick, on the eleventh day of incubation, the sphenoido-frontals exist as a thin 

 osseous scale along each orbital margin ; the bony piece at its widest part extending 

 about a line both above and below the upper orbital boundary. At the same time the 

 parietals are small ovoid patches just above the squamosals, which are already ossified, 

 and fully twice the size of their meta-neurapophyses, the parietals. In the Pigeon, one 



' Owen, Osteol. Catal. vol. i. p. 260. " Edinb. New Phil. Journ. 1857, p. 170. 



' The inter- or temporo-parietals have two centres in the young Dugong, and probably in the ' Lissencephala" 

 at an early age. 



VOL. IV. PART VII. 2 R 



