MR. W. K. PARKER ON THE OSTEOLOGY OF BAL^NICEPS REX. 281 



post-sphenoidal ento- and ecto-pterapophyses ; whilst the basi-sphenoid itself is double 

 its usual size, and looks very much like two coalesced pieces. Observations on the 

 crania of young Insectivora are a great desideratum ; for we shall see that the Ovipara 

 have what might be taken for the centrum of a temporal sclerotome ! 



From our early days we have been in the habit of looking at the lower part of the 

 sphenoido-temporal region in birds as something structurally distinct from the upper — 

 that part which forms the 'sella,' and runs forward as the strong basal beam of the 

 interorbital septum. 



Looking at this region of the skull of the Chick on the eleventh day (a little past 

 the middle of the incubating period), we find three centres to the ' basi-sphenoid,' one 

 mesial and anterior, on the same high plane as the basi-occipital, and two symmetrical 

 pieces below and between these higher osseous centres ; the latter two are developed in 

 the lowest stratum of that basi-cranial cartilage which fills-in the hypophysial space. 

 These cortical ossifications lie exactly between the ossa quadrata, the fenestra ovalis being 

 on a line with the posterior end, the foramen ovale lying over the anterior ; their shape 

 inclines to a right-angled triangle, the bases being opposed to each other. Each of these 

 ossifications is a very thin shell, convex below and somewhat cupped above ; and they 

 never encroach much upon the primordial cartilage, forming (as they do in the adult bird) 

 the thin lower table of the basis crauii, and connected to the single mesial element 

 above by delicate threads of bone and by the osseous canal of the internal carotid. 

 These pieces curve upwards both before and behind ; the basi-occipital is horizontal ; 

 and the basi-sphenoid points steadily upwards, being ultimately anchylosed to the 

 descending plate of the pre-sphenoid in front, and of the connate orbito-sphenoids in 

 the middle, whilst its posterior extremity becomes fused to the basi-occipital, thus ex- 

 cluding the basi-temporals altogether from the cranial cavity. Professor Goodsir {op. cit. 

 p. 15-i) says, " The passage of the anterior acuminated extremity of the centrum be- 

 hind, beneath the lower margin of the pre-sphenoidal centrum, so as to support it, is 

 merely an example of that longitudinal obliquity in the setting on of the cranial cen- 

 trums against one another, which may be considered as the rule rather than an 

 exception." These basi-temporals appear to be another pertinent instance ; yet, after 

 all, they do not necessarily belong to an additional segment of the cranium. 



The anterior margin of these ossific centres continues free throughout life in many 

 birds, the Eustachian canal being completed by membrane ; this is especially the case 

 in Balaniceps, Ardea, and Diomedea. 



In young Rooks of the fourth week the basi-temporal is separate from the basi- 

 sphenoid, and in the adult Merlin {Falco cBsalon) and in the Lapwing {Vanellus cristatus) 

 much of the suture still remains. The external margin of each basi-temporal forms the 

 floor of the tympanic cavity, like the temporal pterapophyses of the Hedgehog and Mole. 

 In the Chick, the ossification of these parts proceeds pari passu with that of the pre- 

 maxillaries ; they have coalesced with each other on the fourteenth day, at which time 



