MR. W. K. PARKER ON THE OSTEOLOGY OF BALZNICEPS 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 bypophysial 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. Hach 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 cranii, 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-occipitat, thus ex- 
cluding the basi-temporals altogether from the cranial cavity. Professor Goodsir (op. cit. 
p. 154) 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 Baleniceps, 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 esalon) 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 pussu with that of the pre- 
maxillaries ; they have coalesced with each other on the fourteenth day, at which time 
