Bauhaus-Universität Weimar

Titel:
The Cyclopaedia of Anatomy and Physiology, vol 1: A-Dea
Person:
Todd, Robert Bentley
PURL:
https://digitalesammlungen.uni-weimar.de/viewer/image/lit25759/322/
AVES. 
310 
the orbit, the external terminates behind the 
middle turbinated lamina in a cul-de-sac. 
These olfactory laminæ 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.) Thecanal, 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, fig. 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 olfactoiy 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,fig. 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 diploë ; 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 : 
(rrallatores, Natatores, Ruptores, Scansores, 
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 VuHures 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. 
lioget 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, Bridgewater Treatise, vol. ii. p. 406.
        

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