OF GALLINACEOUS BIRDS AND TINAMOUS. 179 
part of the conjoined frontals, there is a distinct, oblong, membranous space, com- 
municating freely behind with the antero-inferior fontanelle, caused by the deficient 
growth of the orbital plates of the frontal and the orbital processes of the presphenoid 
(f., p-s.). A certain part, therefore, of the hemispheres and the olfactory lobes are 
merely protected by membrane, as in the early condition of the embryo. The olfac- 
tory crura in their posterior half are separated only by the “ falx cerebri,” where it is 
attached to the small ‘‘crista galli.” Between the antorbital plates, the middle 
ethmoid thickens suddenly ; but anchylosis has produced an apparent confusion in this 
region. On careful examination, however, the different parts may be made out. 
The narrowest part of the coalesced frontals, between and above the eyes, is under- 
propped by the pointed end of the top of the ethmoid, which, further forwards, sends 
outwards a transverse ala on each side, these ale gradually increasing in width until 
they reach the region of the antorbitals. In the early embryo these ale are continuous 
along the top of all the remainder of the soft, chondrifying cranio-facial axis. 
As the skull increases in size considerable differentiation takes place; so that the 
posterior part of each thin, outstanding, and down-turned ‘‘ wing” may not inappro- 
priately be called the aliethmoid, the middle the aliseptal, and the anterior the ali- 
nasal; this last being the rudiment of the ale nasi of the adult bird. The middle 
portion or “‘aliseptal”” turns downwards and inwards to form the “inferior turbinal ;” 
whilst the ‘‘ aliethmoid ” turns down to form the upper turbinal or prefrontal. Look- 
ing at the antorbital plate of the Hemipodius from behind (Pl. XXXIV. fig. 6), we can 
see it to be composed of three portions connected by a faint, triradiate suture. The 
external portion of this relatively large cellular mass of bone is formed by the lachry- 
mal (J.), which is like that of the Pigeon, but still more like that of the Dodo. The 
supero-internal portion is the upper prefrontal (pr.f.); the infero-internal is auto- 
genous in its cartilaginous state, as well as in its ossified condition. This is the 
lower prefrontal, the so-called ‘‘ antorbital”’ (a.0.) of the bird, and the homologue of 
the ‘‘ pars plana,” or ‘‘ lamina papyracea,” of the Mammal. This perirhinal element is 
partly coiled upon itself, in many birds, to form the middle turbinal. 
In Hemipodius these coalesced structures are the tiny counterparts of what we see in 
the Dodo’s skull. The ‘‘ antorbital” mass towards the eyeball is concave; it is the 
inner third, separated from the outer portion by a gentle vertical ridge. Seen from 
the front (Pl. XXXIV. fig. 5), the ethmoid, prefrontals, and lachrymals of Hemipodius 
form a beautiful cellular structure. The great middle ethmoid (p.e.) is of moderate 
thickness, and is carinate anteriorly; it is separated on each side from the oval, 
swollen base of the upper turbinal (¢.) by a very distinct space, through which the pas- 
sage for the olfactory crura can be seen. In front of and somewhat external to these 
smooth, egg-like masses, the ‘‘ aliethmoid” (a.et.) passes forwards, downwards, and 
inwards, as a thin osseous lamina, with its free internal edge dentate. Externally this 
lamina articulates with the front of the tumid lachrymal (/.) down its (vertical) mid 
