6 



CASSELLS BOOK OF BIRDS. 



intelligence necessary for the performance of the important duties entrusted to their charge ; and in this 

 respect, as will be made manifest by a perusal of their history, they occupy a position in the economy 

 of nature fully equal or even superior to that enjoyed by the most favoured quadrupeds. The mental 

 faculties of the parrots correspond with those of the monkeys, whom in their habits and capabilities 

 these birds closely resemble ; in cunning they are quite upon a par with their four-handed neigh- 

 bours, with which, in the forests of tropical 

 countries, they are so generally associated ; 

 and when removed from their native woods, 

 and made, as they often are, the companions 

 of mankind, the facility with which they 

 can be taught to imitate human actions — nay, 

 to mimic our very speech — bears ample 

 testimony to the exalted character of their 

 mental capacities. 



On examining the brain of a bird, the 

 anatomist is therefore by no means surprised 

 to find that, both in its development and in 

 the perfection of its structure, it surpasses 

 that of many quadrupeds. The proportionate 

 volume of the brain of some of our singing 

 birds, as compared with the dimensions of 

 their bod)', is astonishing, and reveals to us 

 at a glance the reason why these little favou- 

 rites are so sagacious and so eminently sus- 

 ceptible of education. (See Fig. 4.) 



In strict correspondence with this exalted 

 condition of their cerebral organisation are 

 the senses whereby they hold intercourse with 

 surrounding nature. Their power of vision 

 is beyond our comprehension, and the elabo- 

 rate contrivances whereby the eye of a bird 

 is adapted to its peculiar mode of life, might 

 furnish materials for a lengthy treatise, imper- 

 fect as is our knowledge of the numerous 

 delicate arrangements demonstrable by ana- 

 tomical skill in every part of its structure. 

 At present we can but briefly allude to a 

 few of the more conspicuous peculiarities 

 wherein the visual apparatus of a bird differs 

 from that of other creatures. 

 The distances from which the vulture and the hawk can see their prey are almost incredible. To 

 have the " eye of a hawk," to see with " eagle glance," are expressions which, though common 

 enough, give but a very feeble idea of the extent to which those birds are gifted in this respect, or of 

 the vast expanse bounded by their horizon. The falcon sees its diminutive prey from an altitude at 

 which it is itself invisible, and from the very sky swoops down upon its quarry with the velocity of a 

 shot, rarely missing its victim, and thus proving at once the perfection of its sight and the steadiness 



Fig. 4. — HEAD OF A SWAN (Cygnus olor). 



1 he upper part of the skull has been removed to show the brain and eyes 

 in sitic. a. a, the Cerebral Hemispheres; b, the Cerebellum; c, the 

 Spinal Cord. All the above parts are represented covered by their 

 investing membranes, e, Sinuses of the Dura Mater ; g, g, Walls of 

 the Skull; h t h, Base of the Beak; «r, Optic Nerve of the Left Eye ; 

 p, p, Large sentient Nerves supplying the Bill: v, Bony Ring in front 

 of the Eye-ball , x, x, Transparent Cornea ; i, 3, 5, 7, Muscles moving 

 the Eye-ball. 



