314 



AVES. 



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 pillars 

 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 (ntjjig. 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,fg. 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: (Jig* 

 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 (jig. 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 (Jiff. 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 Ramphastidfc , 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 b;rd, ob- 

 serves that, notwithstanding M. Button'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, t 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, Jig. 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 Latnelli-rostres. 



* Zool. Journal, vol. iv. p. 464. 



