DEVELOPMENT OF THE SKULL IN THE OSTEICH TEIBE. 131 



does not quite reach the fenestra behind ; has not reached the trabecular region below, 

 but above it has become anchylosed to a great extent to the broad upper bony piece — 

 the connate upper prefrontals (Plate IX. fig. 1, eth.). This latter bone is pear-shaped 

 on its upper, partly exposed aspect (Plate IX. fig. 5, eth.\ the crista galli being nearly 

 hardened by it at its narrow hinder end ; its broad front portion has extended nearly 

 as far as it will extend, into the root of each upper turbinal (Plate IX. fig. 1). Rela- 

 tively, in the adult, it reaches one-third further forwards; then the septal region is 

 cartilaginous for a slight extent (3 lines), and then an equal-sized tract of bone ends it 

 in front. The coalesced ethmoid bones terminate in a nearly straight line in front ; 

 this truncate end leaning backwards below, at which part the rest of the septum is 

 a styliform cartilage an inch in length. Between this lower and the partly ossified 

 upper bar, there is a large notch (Zoological Transactions, vol. v. plate 42, fig. 4, eth. 

 s.n.). We here catch the first glimpse of the important septum nasi of the typical bird. 

 The whole septal region is relatively much smaller in the adult than in the young Rhea. 

 In the young, the vertical ethmoid is a hatchet-shaped ossicle, thickest where the " pars 

 plana " approaches it ; in the old bird an oval fenestra, 6 lines by 4, has been caused by 

 the absorption of the bone above the relatively lessened pars plana, and between the 

 termination of the olfactory crura (see op. cit. plate 42, fig. 4, m.s.). 



I see no turbinal outgrowths on the down- and in-turned upper lamella (Plate X. 

 fig. 9, al.e), but external to the confluence of the huge inferior turbinal with the pars 

 plana there is, inside its elegantly plicate external part (Plate X. fig. 11, p.p), an 

 obliquely vertical oblong outgrowth, which in a sinuous manner turns first inwards and 

 then outwards (Plate X. fig, 10, m.t.b). Both margms of the pai'S plana are free, but 

 above it runs insensibly into the rudiment of the cribriform plate (aliethmoid), and in 

 front and below it is to some degree confluent vidth the funnel-shaped end of the large 

 inferior turbinal (Plate X. fig. 11, i.t.b.). This latter cartilage has its root in the septal 

 region, all along from the upper turbinal to the commencement of the alse nasi (Plates 

 IX. & X. al.s.). The simple aliethmoidal lamella turns inwards, where it receives the 

 olfactory filaments and protects the bulb (Plate IX. fig. 2, & Plate X. fig. 9, ale.) ; 

 as soon as this cartilage expands again it has become the root of the inferior (anterior) 

 turbinal. This ala of the septum stretches out some distance, then curls round a little, 

 then splits into two lamellae (Plate X. figs. 14, 15), the outer of which forms the semi- 

 cylindrical wall of this part of the nasal labyrinth ; the inner lamella [i.t.b.) turns 

 abruptly inwards, coiling itself into a most beautiful scroll, with three complete turns 

 of the spire. This inferior turbinal scroll is half an inch in length m the ripe pullus ; 

 the scroll is, at its middle, 2 lines in diameter ; a shallow fossa passing fi-om above, 

 rather suddenly backwards, shows from the outside where the egg-shaped alinasal fold 

 begins (Plate IX. figs. 1-3, al.n.). This lamina, continuous with the last, is not simple, 

 but the secondary plait which arises within it, and which turns inwards, bifurcates, 

 one plait half the width of the other, turning upwards and outwards, the other down- 

 wards and outwards (Plate X. fig. 16). Inside this double lamella (the alinasal turbinal) 



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