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/lit25759/326/
AVES. 
314 
the beak, in consequence of the union which 
takes place between different small fibres as 
they pass from the circumference inwards. It 
is worthy of observation that the principle of 
the cylinder is introduced into this elaborate 
structure : the smallest of the supporting pdlars 
of the mandibles are seen to be hollow or 
tubular when examined with the microscope. 
The structure is the same in the lower man¬ 
dible {m, fig. 150), but the fibres composing 
the net-work are in general stronger than those 
of the upper mandible. 
The medullary membrane lining these cavi¬ 
ties appears to have but a small degree of 
vascularity. Processes of the membrane, ac¬ 
companying vessels and nerves, decussate the 
conical cavity at the base of the beak. The air is 
admitted to the interior of the upper mandible 
from a cavity {b, fig. 150) situated anterior to 
the orbit, which communicates at its posterior 
part with the air-cell continued into the orbit, 
and at its anterior part with the maxillary 
cavity. The nasal cavity is closed at every 
part except at its external and internal aper¬ 
tures by the pituitary membrane, and has 
no communication with the interior of the 
mandible. * 
The horny sheath of the mandibles in the 
Hornbills and Toucans is so thin that it often 
becomes irregularly notched at the edge from 
use. The Hornbills have, besides, upon their 
enormous beak, horn-like prominences of the 
same structure and of different forms, the use 
of which is not known. 
The Trogons, Touracos, Buccos, &c. exhibit 
forms of the bill which are intermediate to that 
of the large but feeble bill of the Toucans, and 
the short, but hard, strong, and broad bill of 
the Parrot-tribe, which is also hooked, so as 
to assist in climbing, like a third foot: (fig. 
128.) 
The short, conical, and vaulted beak of the 
Rasores (fig. 121) serves to pick up with due 
rapidity the vegetable seeds and grains which 
constitute their food, as well as small insects, 
as ants, &c. with which the young are frequently 
nourished. 
The bills of the small Insessorial or Pas¬ 
serine birds present every gradation of the 
conical form, from the broad-based cone of the 
Hawfinch to the almost filamentous cone of the 
Humming-birds (fig. 117, 125), and each of 
these forms influences the habits of the species 
in the same manner as in the larger birds. The 
short and strong-billed Insessores live on seeds 
and grains ; those with a long and slender bill 
on insects or vegetable juices. If the slender 
bill be short, flat, and the gape very wide, as 
in Swallows, the bird takes the insects while 
on the wing (fig. 118) ; if the bill be elongated 
and endowed with sufficient strength, as in the 
Hoopoes, it serves to penetrate the soil and 
pick out worms, &c. 
Of all bills, the most extraordinary is that of 
the Cross-bill, in which the extremities of the 
mandibles curve towards opposite sides and 
* See Anatomical Appendix to Gould’s Mono¬ 
graph on the Ramphastidœ, fol. 
cross each other at a considerable angle—a dis¬ 
position which at first sight seems directly 
opposed to the natural intention of a bill. 
With this singular disposition, the Cross-bill, 
however, possesses the power of bringing the 
points of the mandibles into contact with each 
other ; and Mr. Yarrell, in his excellent paper 
on the Anatomy of the Beak of this bird, ob¬ 
serves that, notwithstanding M.Buffon’s asser¬ 
tion to the contrary, it can pick up the smallest 
seeds, and shell or husk hemp and similar 
seeds like other birds. He further shows that 
the disposition and power of the muscles is such 
that the bill gains by its very apparent defect 
the requisite power for breaking up the pine- 
cones that constitute its natural food. In a 
pair of Cross-bills which were kept for some 
time in captivity, one of their principal occu¬ 
pations, Mr. Yarrell observes, “ was twisting 
out the ends of the wires of their prison, which 
they accomplished with equal ease and dexterity. 
A short flat-headed nail that confined some 
strong net-work was a favourite object upon 
which they tried their strength, and the male, 
who was usually pioneer in every new exploit, 
succeeded, by long-continued efforts, in draw¬ 
ing this nail out of the wood, though not 
without breaking off the point of his beak in 
the experiment. Their unceasing destruction 
of cages at length brought upon them sentence 
of banishment.’' He concludes his memoir by 
observing that “ the remarks of Buffon on the 
beak of this bird, which he characterizes as 
‘ an error and defect of nature, and a useless 
deformity,' exhibit, to say the least of them, 
an erroneous and hasty conclusion, unworthy 
of the spirit of the science he cultivated. 
During a series of observations on the habits 
and structure of British Birds, 1 have never 
met with a more interesting or beautiful ex¬ 
ample of the adaptation of means to an end 
than is to be found in the tongue, the beak, 
and its muscles, in the Cross-bill.” * 
The tongue, as has been already observed, 
can hardly be considered as an organ of taste 
in Birds, since, like the mandibles, it is gene¬ 
rally sheathed with horn. It is principally 
adapted to fulfil the offices of a prehensile 
organ in association with the beak, and it pre¬ 
sents almost as many varieties of form. Orni¬ 
thologists have not yet perhaps derived all the 
advantages which a study of the modifications 
of the tongue might afford in determining the 
natural affinities of birds. 
The os hyoides very much resembles that of 
Reptiles. Its parts have been minutely studied 
by Geoffroy St. Hilaire, who has bestowed 
upon them separate names: (a,fig. 151) is the 
glosso-hyal, b the basi-hyal, d d the apo-hyals, 
e e the cerato-hyals, c the uro-hyal. The 
body, or basi-hyal element, is more thickened 
than the rest : in some birds it is cylindrical. 
The length of the tongue depends chiefly on that 
of the lingual process or glosso-hyal element. 
In most birds it is lengthened out by a carti¬ 
lage a' appended to its extremity. This is re¬ 
markable in the Swan and other Lamelli-rostres. 
* Zool. Journal, vol. iv, p. 464.
        

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