B I R 



tlie classes of mammifers, birds, and reptiles. Dr. Sbai |..-\ s 

 obscnrations confirm their discovery of this ciliary motion, 

 with the following modifications, viz., in the air-passages and 

 Fallopian tube* of mamroifors, in the air-passages of birds, 

 and in the mouth and throat of the batrachians ; the nega- 

 tive observations respecting the oviduct of the bird being 

 inconclusive. 



Brain, Nervout Syttan, and Sentet. 

 We must now turn our attention to that part of the ani- 

 mal economy wherein resides the intelligence which directs 

 and regulates the whole of the voluntary powers. The 

 brain of birds possesses the same characters which arc to 

 be found in other oviparous vcrtebrated animals, but its 

 proportional volume is its distinguishing peculiarity ; and 

 this volume often surpasses the development of that organ 

 in mammifers. Indeed, in some birds, and more particu- 

 larly in some of the songsters, the brain has been said to 

 exceed that of roan when considered in reference to the 

 size of the head and of the whole body. But this assertion, 

 after all, involves a fallacy. The size of the eye regulates 

 the development in great measure ; and when we look at 

 the relative proportion of brain in a canary bird, we must 

 not forget the great lightness of the other parts of its body. 

 In a herring a part of the brain is as much developed in 

 proportion as the same part is in man. The following scale 

 has been given as an example of the size of the brain in 

 relation to that of the body : 



Eagle, 1 -260th of the body ; sparrow, l-25tb ; chaffinch, 

 l-27th; redbreast, l-32nd; blackbird, l-68th ; canary- 

 bird, l-14th ; cock, l-25th; duck, l-257th; goose, l-360th 

 In man the brain forms from l-22nd to l-33rd of the body 

 in some apes, l-22nd ; in the elephant, 1-SOOth ; in the 

 horse, l-400th ; in the dog, 1-lfilth ; and in the cat, l-94th 

 The size of the brain in birds arises principally from la 

 berries analogous to the corpora ftriata of mammifers, am 

 not from the hemispheres, which are small, smooth, am 

 without convolutions. The cerebellum is large, almos 

 without lateral lobes, and formed principally by the vermi 

 form process. Several parts found in the brain of mom 

 mifers are absent in birds, and among these are the corpui 

 calhtum and pom Varolii. With reference to the compara 

 tive size of the brain in birds, it may be necessary to say a 

 few words. From the days of Aristotle down to a very late 

 period it was received and transmitted as an axiom that man 

 has the largest brain in proportion to his body. The spiri 

 of modern investigation, however, soon discovered severe 

 exceptions to this rule, and destroyed the generally admittet 

 (inclusion. Then came Summering, to whom we owe tin 

 great bulk of our information on this subject, and he pre 

 sented us with the ratio which the mass of the brain bear 

 to the nerves which it gives off; a point of comparison whicl 

 still holds good. ' Let us,' writes Lawrence in his edition 

 of Blumenbach's Comparative Anatomy, ' divide the brail 

 into two parts ; that which is immediately connected will 

 the scnsorial extremities of the nerves, which receives thci 

 impressions, and is therefore devoted to the purposes o 

 animal existence. The second division will include the res 

 of the brain, which may be considered as connecting th 

 functions of the nerves with the faculties of the mind. Ii 

 proportion, then, as any animal possesses a larger share o 

 the latter and more noble part that is, in proportion as the 

 organ of reflexion exceeds that of the external senses may 

 we expect to find the powers of the mind more vigorous and 

 more clearly developed. In this point of view man is de- 

 cidedly pre-eminent ; here he excels all other animals that 

 have hitherto been investigated.' 



Of the five senses which are on the watch to give infor- 

 mation to the scnsorium, sight, smell, and hearing are most 

 acute in birds. 



Sight. We have seen that the bony orbits arc of great 

 magnitude, and the organs of sight which are contained 

 therein are proportionably large. In the birds of prey the 

 orbits have the shape of a ' chalice,' says Blumenbach, 

 or cup used in the communion service. The cornea, 

 which is very convex, forms the bottom of the cup, and the 

 posterior segment of the sclerotica resembles its cover. This 

 peculiar form arises from the curvature and length of the 

 bony plates, which, as in all other birds, occupy the front of 

 the sclerotica, lying close together and overlapping each 

 other. These bony plates form in general a flat or slightly 

 convex rine ; being long and curved in the aedpitm 

 (hawks) they form a concave ring, which gives the whole 



n i R 



ycball the above-mentioned form.' Ry means of this ring 

 he ! u kind of self-adjusting telcM-opo, s 



ake in both near and very distant obi' 



[Sclerotic plain of Potfuio.] 



A representation of the sclerotic plates, forming the bony 

 ring in the eye of the penguin (Aptenodytes), is here given. 

 They remind us forcibly of the eye-plates in some of the 

 reptiles, particularly of those belonging to the eyes of the 

 Enaliosaurians, or fossil marine lizards. The penguin has 

 to adjust its eye for vision both on land and under water. 

 This contrivance must greatly assist the adjustment neces- 

 sary for seeing clearly in such different media. 



The crystalline humour is flat in birds; and the vitreous 

 humour is very small. The colour of the iris varies in dif- 

 ferent species, and in many cases is very brilliant. The 

 martupium, which arises in the back of the eye, and the 

 use of which is not very clearly ascertained, is a peculiarity 

 in the eye of birds. They have three eye-lids, two of which, 

 the upper and lower, are closed in most of the race by the 

 elevation of the lower one, as may be frequently seen in our 

 domestic poultry. The owl, the goat-sucker, and a few 

 others, have the power of depressing the upper eye-lid. Of 

 these birds the upper only is furnished with eye-lashes 

 generally : the ostrich, secretary vulture, some parrots, and 

 a few other birds, have them in both lids. But the third 

 eye-lid, or nictitating membrane, forms the most curi- 

 ous apparatus. When at rest, this, which is a thin semi- 

 transparent fold of the tunica conjunctiva, lies in the inner 

 corner of the eye, with its loose edge nearly vertical. By 

 the combined action of two muscles which are attached to- 

 wards the back of the sclerotica, it is capable of being 

 drawn out so as to cover the whole front of the eye-ball like 

 a curtain, and its own elasticity restores it to the corner in 

 which it rested. This, it is said, enables the eagle to look 

 at the sun : it may be seen in operation to much advantage 

 in the Great South American Eagle (Harpyia destructor) 

 at the gardens of the Zoological Society in the Regent's 

 Park. 



The sense of hearing appears to be sufficiently acute in 

 birds, though (with the exception of the night-birds, the 

 owls in particular) they have no external cartilaginous ear; 

 and the peculiar valve, partly muscular, partly membranous, 

 placed at the auditory opening even in those birds, has none 

 of the development which generally marks the concha of 

 mammifprs. The peculiar arrangement of the compara- 

 tively loosely barbed feathers, however, round the aperture 

 (meatut auditorius) compensates for it ; and this arrange- 

 ment may be well seen in the rapacious birds. The mem- 

 brane of the drum (membrana tympani) is convex exter- 

 nally, and the drums of both ears are connected by the 

 air-cells of the skull. There is neither malleus nor stapes, 

 and their place is supplied by a single auditory bone (ossi- 

 culum tiiulitii\) which connects the membranes of the drum 

 with ihefenestra ovalis. The Eustachian tubes terminate 

 in a sort of common aperture on the concavity of the palate. 

 The labyrinth is without a cochlea ; instead of which there 

 is a short, blunt, hollow bony process obliquely directed 

 backwards from the vestibule, and divided into two portions, 

 one of which end* at ihefenestra rotunda. 



The sente of smelling in the majority of birds seems to be 

 highly developed. The olfactory nerve is given off from the 

 foremost part of the front lobe of the bniin, whence it passes 

 along a canal to the nose, and is ramified on the pituitary 

 membrane, which is spread over two or three pairs of bony 

 or cartilaginous concha; narium. The nostrils terminate in 

 different parts of the upper mandible in different genera; 

 and, according as these apertures are smaller or larger, or 

 more or less covered by membranes, cartilages, feathers, or 

 other integuments, the sense is probably more or less acute. 

 But no bird is without nostrils, though Buffnn asserts that 

 several are unprovided with them : the puffin, indeed, and 

 some others have them so small, and placed so closely on 

 the margin of the mandible, that they are not easily de- 

 tected. 



