150 ME. "W. K. PAEKER ON THE STRUCTIJRE AND 



cartilaginous plates (Plate XII. fig. 7, al.e., eth.) ; in the adult the bone grows down- 

 wards and inwards, and then stops, leaving the rest soft. To one fresh from the study 

 of the nasal labyrinth in the Mammals, the extreme simplicity of the olfactory region in 

 the Emu would be very perplexing ; to one fresh from the study of this part in the lower 

 Vertebrata, the complexity of that part of the nose of the Emu which is supplied by 

 the fifth nerve would be just as strange. There is no discontinuity of the nasal carti- 

 lages in the Emu (Plate XII. fig. 7), such as we see in the higher birds, and yet the 

 regions are not ill-defined. The three turbinals of Man and his alae nasi supply us with 

 familiar conceptions, and the ordinary works on human anatomy with familiar terms, 

 yet these may be modified a little to suit wider groups, and the necessities of a fuller 

 morphology. 



The terms which I have been in the habit of using (see Zool. Trans, vol. v. pp. 149- 

 242) are for the homologue of the upper turbinal " aliethmoid," for the middle " antor- 

 bital," or sometimes the old term " pars plana," for the root of the inferior turbinal 

 " ali septal," and " alinasal" for the alee nasi. 



When the turbinals of the Emu are seen from within (Plate XII. fig. 7, u.th), the 

 upper one looks to have a very large development ; it is all hollow, and simple, however 

 (Plate XII. fig. 8) ; for the aliethmoid, after growing outwards, turns round, and grows 

 towards the axis of the skull ; in doing so it grows upwards also, in a rounded manner. 

 It then keeps (for some distance downwards, and much more in front than behind) near 

 the perpendicular ethmoid, then makes a semicylindrical curve outwards ; the lower 

 edge of this outward part being continuous with the top of the pars plana (antorbital). 

 In a vertically transverse section this simple cartilage presents the form of the letter S 

 (Plate XII. fig. 8), there being a deep concavity on the inside, at the top ; then a large 

 convexity ; then a deep, almost cylindrical groove separating the upper from the lower 

 turbinal. On the outside the upper part is a semicylinder, then a flask-shaped cavity, 

 with the neck behind, and then below it is the swelling top of the middle ethmoid. 

 Seen from within, the upper turbinal looks like a miniature bagpipe with the broad end 

 forwards (Plate XII. fig. 7). This is really the homologue of the cribriform plate (as 

 well as of its turbinal outgrowths) of the Mammal ; but here there is no sieve-like 

 structure, and there are no lamellar outgrowths. 



Close as we now stand to the Mammal, it is yet very hard to see the exact bearings of 

 this subject: the present Hunterian Professor of Anatomy did once, with his keener 

 insight, give the writer a clue to trace its mazes by ; it has, however, required much per- 

 sistent work to make it clear. The hole through which the olfactory cms of the bird 

 passes out of the cranium into the orbit, is not a single representative of the many pores 

 through which the olfactory filaments of the Mammal pass ; the membrane which encloses 

 that crus is really part of the skull-floor ; and the chink through which the olfactory cms 

 passes anteriorly, between the aliethmoid and the perpendicular plate, is the homologue 

 of that vertical series of passages which lies nearest the crista galli of the Mammal. In 

 the bird this chink is not subdivided, and the crus passes in to give off its filaments from 



