310 



AVES. 



the orbit, the external terminates behind the 

 middle tu/binated lamina in a cul-de-sac. 

 These olfactory laminae differ in regard to tex- 

 ture. In the Cassowary and Albatross they 

 are said to be membranous. Cuvier states that 

 they appeared to him to be bony in the Horn- 

 bill and Toucan. We have found this to be the 

 case in the recent Toucan. The organ of smell in 

 this singular species is confined to the base of its 

 enormous beak, (d,e,fig. 150.) The canal, which 

 is traversed by the air and odorous particles in 

 inspiration, forms a sigmoid curve in the vertical 

 direction. The external orifice is on precisely 

 the same perpendicular line as the internal, 

 or, as it is generally termed, the posterior nasal 

 aperture. The external nostril (d, Jig. 150) 

 being situated on the posterior surface of the 

 upper mandible, where it is raised above the 

 level of the cranium, is consequently directed 

 backwards, secure from all injury to which it 

 might be exposed while the bill was used in 

 penetrating dense and interwoven foliage. 

 The olfactory canal is at its commencement 

 of a cylindrical form, and about two lines in 

 diameter. It passes forwards for about half an 

 inch, receiving the projection of the first spongy 

 bone, then bends downwards and backwards, 

 and is dilated to admit the projections of the 

 two other spongy bones. From this point it 

 descends vertically to the palate, at first con- 

 tracted and afterwards dilating to form the in- 

 ternal or posterior orifice, (e,Jig. 150.) The 

 first or outermost spongy bone is almost hori- 

 zontal, and has its convexity directed outwards. 

 The second is nearly vertically placed, with its 

 convexity directed backwards : it terminates in 

 a narrow point below. The superior spongy 

 bone is about the size and shape of a pea. 

 All these bones are processes from the inner 

 and posterior parietes of the nasal passage; 

 they are cellular, and air is continued into 

 them from the cranial diploe ; but the parietes 

 of the nasal passage are entire and smooth, 

 and lined by a delicate pituitary membrane, so 

 that there is no direct communication between 

 the cells, the turbinated bones, or of the man- 

 dible and the nasal passages. 



In most birds the nasal cavities communicate 

 with the pharynx by two distinct but closely 

 approximated apertures. In the Cormorant, 

 however, these join into one before their termi- 

 nation posteriorly, which is consequently by a 

 single aperture. The olfactory nerves are dis- 

 tributed exclusively to the pituitary membrane 

 covering the septum narium and the superior 

 spongy bone. The pituitary membrane is of 

 the most delicate structure, and is most vas- 

 cular, where it covers the superior turbinated 

 lamina, and becomes thicker and more villous 

 as it descends upon the middle one. It every- 

 where displays numerous pores of muciparous 

 glands, which bedew it with a lubricating 

 secretion. 



According to Scarpa the acuteness of smell 

 is exactly in proportion to the development of 

 the superior turbinated lamina, to which the 

 size of the olfactory nerve corresponds. The 

 following is the order in which, according to 



his experiments, birds enjoy the sense of smell, 

 beginning with those in which it is most acute : 

 Grallatores, Natatores, Raptores, Sccmsores, 

 Insessores, Rasores. 



There is still, however, much obscurity 

 with reference to the extent to which Birds 

 make use of their olfactory organs. It has 

 been generally asserted that birds of prey are 

 gifted with a highly acute sense of smell, and 

 that they can discover by means of it the 

 carcass of a dead animal at great distances ; 

 but those who have witnessed the rapidity with 

 which the Vultures descend from invisible 

 heights of the atmosphere to the carcass of an 

 animal, too recently killed to attract them by 

 putrefactive exhalations, have generally been 

 led to consider them as being directed to their 

 quarry by sight. " That this is the case," Dr. 

 Koget observes, " appears to be now suffi- 

 ciently established by the observations and 

 experiments of Mr. Audubon, which show that 

 these birds in reality possess the sense of smell 

 in a degree very inferior to carnivorous quadru- 

 peds, and that so far from guiding them to 

 their prey from any distance, it affords them no 

 indication of its presence even when close at hand . 

 The following experiments appear to be perfect- 

 ly conclusive on this subject. Having pro- 

 cured the skin of a deer, Mr, Audubon stuffed 

 it full of hay ; after the whole had become 

 perfectly dry and hard, he placed it in the mid- 

 dle of an open field, laying it down on its back 

 in the attitude of a dead animal. In the 

 course of a few minutes afterwards he observed 

 a vulture flying towards and alighting near it. 

 Quite unsuspicious of the deception, the bird 

 immediately proceeded to attack it as usual in 

 the most vulnerable points. Failing in this 

 object, he next with much exertion tore open 

 the seams of the skin where it had been stitched 

 together, and appeared earnestly intent on get- 

 ting at the flesh, which he expected to find 

 within, and of the absence of which not one 

 of his senses was able to inform him. Find- 

 ing that his efforts, which were long reiterated, 

 led to no other result than the pulling out large 

 quantities of hay, he at length, though with 

 evident reluctance, gave up the attempt, and 

 took flight in pursuit of other game to which 

 he was led by the sight alone, and which he 

 was not long in discovering and securing. 



" Another experiment, the converse of the 

 first, was next tried. A large dead hog was 

 concealed in a narrow and winding ravine, 

 about twenty feet deeper than the surface of 

 the earth around it, and filled with briers and 

 high cane. This was done in the month of 

 July, in a tropical climate, where putrefaction 

 takes place with great rapidity ; yet, although 

 many vultures were seen from time to time 

 sailing in all directions over the spot where the 

 putrid carcass was lying, covered only with 

 twigs of cane, none ever discovered it; but in 

 the meanwhile several dogs had found their 

 way to it and had devoured large quantities of 

 the flesh."* 



* See Roget, Bridgcwater Treatise, vol. ii. p. 406. 



