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 gaUi." Between the aatorbital 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 alse gradually increasing in width until 

 they reach the region of the antorbitals. In the early embryo these alse 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 alse nasi of the adult bird. The middle 

 portion or " ahseptal" 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 (PI. 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 {I.), 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.o.) of the bird, and the homolo°-ue 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 (PI. 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 (t.) 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 



