132 ANATOMY OF VERTEBRATES. 



gristly, or bony, and in different proportions. The latter is 

 their texture in the Toucan, in which the olfactory organ is 

 confined to the base of the huge upper mandible, fig. 53, d, e, the 

 meatus describino- a vertical sigmoid curve. At its commencement 

 it is cylindrical, then dilates forward to receive the outermost tur- 

 binal, and bends backward to admit the projection of two ethmo- 

 turbinals : after which it descends vertically to the palate, e. The 

 pituitary lining of the meatus is not continued or reflected into 

 the contiguous pneumatic structure of the bill, a, h. 



In most Birds the nasal passages communicate with the palate 

 and pharynx by two distinct but contiguous apertures : in some, 

 e. g., the Cormorant and Gannet, the passages unite and terminate 

 by a single aperture. 



The olfactory nerves are distributed to the pituitary mem- 

 brane of the septum narium, and of the superior and middle, or 

 ethmo-, turbinals ; the lower turbinals being supplied by the fifth 

 nerves. The membrane is most vascular and delicate on the ethmo- 

 turbinals ; and these acquire an unusual size in the Apteryx, 

 where they are attached to the whole outer part of the prefron- 

 tals, answering to the ' os planum,' which makes a large convex 

 projection between and beloAV the orbits. This bird appears 

 to be guided by the sense of smell to the worms that form its 

 food, the outer nostrils being at the end of the long probe-shaped 

 bill. The olfactory nerves are proportionally largest in the 

 Apteryx, and are sent ofl" in numerous filaments from the rhinen- 

 cephalon, by a cribriform plate, to the nose. The extinct Dinornis 

 had a similar developement of the organ of smell. In the Vulture 

 the olfactory nerve is single on each side, and continued from an 

 olfactory ganglion, or * rhinencephalon,' along the upper part of 

 the interorbital space to be distributed upon an upper and middle 

 turbinal, the latter being the largest. In the Turkey the 

 olfactory nerve is one-fifth the size of that in the Vulture, and 

 is ramified on a small middle turbinal, there being no extension of 

 the pituitary membrane over a superior, or ethmo-turbinal.^ This 

 result of comparative anatomy, and the observed differences in 

 the habits and food of the Vulture and Turkey, point to the 

 greater importance and exercise of the sense of smell in the 

 carrion-eating raptorial bird. But it has been sought to invalidate 

 the inference by certain well-known experiments. Mr. Audubon 

 exposed the skin of a deer, stuffed with hay, and in a few minutes 

 a Vulture flew towards and alighted near it, attacked the seeming 

 carcass in the usual way, and tore open the seams of the skin ; 



' XXX1-. p. 34. 



