THE MAMMALIA.— MAN AND BEASTS. 3t> 



Mammalia, and these are lean and meagre. The Rodentia generally possess the optical instruments. The Retina, or expanded extremity of the optic nerve, is the 



largest proportional Brain, and the Pachydermata the smallest. It is very difficult, immediate seat of sensation. Upon this delicate membrane, an inverted picture of 



if not impossible, to arrive at these results with any great degree of accuracy, because the external scene is exactly delineated; and though scarcely half an inch in diameter, 



the weight of the brain generally remains the same, while that of the body will vary it contains the forms, positions, and colours of the most distant objects, without confu- 



considerably according as an animal is lean or fat. sion or irregularity. 



^ , , , ^ , „ . . The black pigment of the Eye is wanting in that variety of the Human race 



The oronortion which the Cerebrum bears to the Cerebellum is, m „,.,.. j ^u- j c • • ^ i -.i. ^t. . c , • ■ ■ , 



lue piupuji.!" called Albmos, and this deficienity is connected with the want of colouring principle 



The Squirrel Monkey {Callithrix sciureus), . . as 14 to 1 .^ ^^^ j^^^_ ^^^ ^^^^.^^ jj^^^^^ ^^^ ^^^^^^ ^^ sometimes found to possess this 



IVian, ,...--•••••" ••• peculiarity when they are said to be glass-eyed. They are capable of transmitting 



The Ox (Bos taurus), y ... -j. ^^ ^^^^^ posterity, and thus forming a breed of white animals. The Ferret's eye 



Dog {Canis familiaris), 8 ... 1 -^ naturally destitute of the black pigment, 



"Wild Boar {Sus scropha), 7 ... 1 j^^ immediate object of vision is colour, and to this alone its function was origin- 

 Horse (Equus cahallus), 7 ... 1 ^^y confined. By habit and by comparison with the other senses, but especially 



Cat (reus catus), . , . - . • ... t) ... 1 ^.j^.^^ ^^^j, of t^om-h, it acquires new powers; and the coloured canvas of original per- 



Hare (Lepus timidus), . . • b...l ception is embodied into a real scene, in which the distance, magnitude, and figures 



bheep (fVyis aries;, . . • . - . ... ■•• of objects may be, in general, instantaneously discovered. This remarkable fact was 



Mouse {Mu^ musculus), 2 ... 1 ^^^^^ estabhshed by Rlr Cheselden, who couched the eyes of a young gentleman born 



«* It is a common opinion," observes Dr Herbert Mayo, *' that the front of the blind, and ascertained the effects produced on the mind by the first exercise of the 



brain is the seat of the intellectual faculties; yet in Monkeys and in Man the back power of vision. 



part of the brain is that which has the largest relative size. The sheep, on the other By certain exquisite contrivances, the Eye is so constructed as to correct the de- 

 hand, has an ample front to its brain, a large intellectual region, according to the fects which Opticians experience in their own artificial instruments. But the consi- 

 phrenolopical theory, while its instinct of attachment to its young has a poor locality deration of the Spherical, Paralactic, and Chromatic Aberrations of light, belongs 

 in its moderate posterior cerebral lobe. Has nothing then been discovered to mark more properly to the science of Optics. 



an essential superiority in the brain of Man? The question must, I believe, be In the Jlammalia, the eye is composed of the same coats and humours as In Man, 

 answered in the negative. No physical condition, distinguishing the human brain being only slightly modified and adapted to surrounding circumstances. The eyes of 

 from that of animals, and therefore fitting it to co-operate with a rational soul, has as the Cetaceous tribes more nearly resemble those of Fishes, as they are flattened on the 

 yet been ascertained, or even plausibly conjectured to exist." anterior side, and adapted to the dense medium in which they reside. By the eiqui- 

 Physiologists have been led, in all ages, by that marked superiority of mental power site arrangement of the sclerotic coat and cornea in the Seal tribe, these animals are 

 which Man possesses above the other animals, to seek in the structure of their brains able to adapt their vision to the two diiFeront media of air and water; and they are 

 for some corresponding difference. It was long supposed that I\Ian has the largest enabled to shorten or elongate the axis of tlie eye according to circumstances. The 

 brain in comparison to his body; but the above Tables show that he is surpassed by eye of the Mus typhlus, or BUnd Rat, is not larger than a poppy seed, and is alto- 

 several Quadrumana, and by the Mouse. gether covered with hair, so that the animal can scarcely perceive the difi^t^renoe 

 There is another point of comparison wliich seems to approach nearer to their actual between light and darkness. The eyes of the Mole are so minute that most persons 

 comparative intelligence, which was first proposed by Summering. By comparing the imagine them to be entirely absent. The pigment at the back of the eye receives the 

 quantity of the brain with that of the nerves arising from it, we ascertain more name of the Tapetum lucidum ; it is of different colours in different animals. 



accurately the degree in which its purer intelligence excels its mere animal nature. \^ the Monkey it is dark -coloured. 



'* Let us divide the brain into two parts; that which is immediately connected with Qx .... creen. 



the sensorial extremities of the nerves, which receives the impressions, and is there- Sheep, pale yellow. 



fore devoted to the purposes of animal existence. The second division will include Rabbit, Hare, and Ho"- .... brown. 



the rest of the brain, which may be considered as connecting the functions of the Ljon, Bear, Cat, and Dolphin, . . pale golden yellow. 



nerves with the faculties of the mind. In proportion, tlicn, as any animal possesses a Dog, Wolf, and Badger, .... pure wliitc, fringed with blue. 



larger share of the latter and more noble part— that is, in proportion as the organ of Horse, Goat, Stag, and Buffalo, . . silvery blue, changing to violet. 



reflexion exceeds that of the external senses — may we expect to find the powers of the t . » » , , , m ,i , - , , ,. . , 



, ,,,,*, T,. A. ,,. It has been supposed that the Tapetum enables these ammals to see more distinctly 



mind more vigorous and more clearly developed. In this point of view Man is . , , , 



- , 1 1 11 1 • 1 1 ■ , 1 , •" *-"*^ dark, 

 decidedly pre-emmcnt; here he excels all other annnals which have hitherto been 



investigated." Sommering found that the brain of JIan never weighed less than 2 lb In the Ear a cavity is always found called the Tympantim or Ear-drum, 



5^ oz., while that of the Horse never exceeded 1 lb. 4 oz. in weight. But the nerves which communicates with the hinder part of the mouth hy a canal called 



arising from the brain of the Horse were at least ten times larger than those in jj^^ Eustachian tuhe. This cavity is closed externally by a membrane. 



However ingenious this theory may be, it is not found to hold good in every termed tile me».6ra«« /^m;7a«/, and contains within it a chain of four bones, 



instance; and even if proved, it would still leave the nature of the union between called the Malleus, or Hammer Bone; the Incus, or Anvil; the Os Orbi- 



ilind and Matter as mysterious and as incomprehensible as ever. culare, or Lenticular Bone; and the Stapes, or Stirrup. The Stapes 



The nerves of the Mammalia bear a striking resemblance in their disposition to rests upon a vestibulum or central porch, which leads on the one side to 



those of Man, with the exception of the olfactory nerves, which are laree and hollow ,i ■ * i ^ j .u i.i .^ r^ i i ■ i i 



'. - 1 1 , 1 , , . b^ *^ •" iiuuu« three semi-circular canals, and on the other to a Cochlea, or spiral canal, 

 processes of the anterior lobes of the cerebrum, the cavities of which communicate 



with the lateral ventricles of the brain. "^^'^''^h communicates by one extremity with the vestibulum, and by the 



^, . . ■ , 1 1 1 ■ 1 • , . , . . other with the Tympanum. 



Their eyes, invariably placed in their orbits, and preserved by two eye- 

 lids and the vestige of a third, have their crystalline humour' preserved The Vestibule, Cochlea, and semi-circular canals, collectively form the Labyrinth. 

 , . ... 11. . ^ . , ,. . Tiiis is the essential part of the orp'an ; and no obstruction or removal of the external 

 by the ciliary process, and sclerotic coat, composed of simple cellular , u .u j . ^i, ex.- i .u t i ■ ... 

 ^ •' ^ ' r r *■ parts can altogether destroy the sense of hearing as long as the Labyrinth remains 



SUDStailce. uninjured. The precise uses of these several parts are not yet fully understood. 



The eye-ball of Man is nearly globular, and about one inch in diameter. It is "^'"^ M^immalia do not appear to be capable of distinguishing musical sounds with 



defended externally by a white opaque membrane, having the density of tanned leather, '''^' nicety, or of deriving that extent of enjoyment which has been bestowed on Man. 



called the Sclerotica, which surrounds every part, excepting the small circular por- "^^^ '^"S ™^y he trained to distinguish one particular tune from another; but the 



tion in front called the Cornea, and a small perforation behind to admit the optic extent of his pleasure or acquirements seems greatly limited. But Man, besides being 



nerve into the brain. The Cornea is perfectly transparent and possesses ■rreat sensi- '■"^^ '° perceive differences between acute and grave tones, is capable of distinguishing 



bility ; yet at the same time it is so tough, as to offer a powerful resistance to external ^°"'" "'' ''^^ hundi-ed varieties in their quality and intensify. A flute, hautboy, and 



injury. Within the Cornea, and immediately in contact with it, is placed a small violincello may all sound the same note, and yet the peculiar quahty of each mcy be 



quantity of pellucid fluid called the Aqueous humour, which occupies the external readily perceived. An attentive ear will observe some differences although twenty 



visible portion of the Eye. The Iris is situate behind the Cornea and the Aqueous human voices sound the same note, and with equal strength; nay, even the same voice 



humour. It consists of a circular membrane, perforated by a small hole in the centre "^y ^^ '^'aried in many ways, by sickness or health, youth or age, leanness or fatness, 



called the Pupil. The colour of the Eye resides in this membrane and both its S°°'' '"' ^^^ humour; and the same words spoken by foreigners and natives, or even 



structure and functions are very remarkable. It is formed of two layers of fibres ■ in ^^ *^® inhabitants of different provinces in the same nation, will be readily distin- 



the one, they are arranged hke rays from the inner to the outer margin; and in the guished. 



other, they form concentric circles. By the action of the radiated fibres the pupil is "^^ ascertain the effect of the high and low notes of the piano-forte upon the Ele- 



contracted ; but it is dilated by the action of the circular fibres. These delicate motions phant and Lion, Sir Evcrard Home procured one of Broadwood's piano-fortes to 



»re executed m a manner which human ingenuity in vain attempts to equal. The make the experiment at the Menagerie in Exeter Change, London. The Elephant 



pupil instantly contracts when exposed to a strong hght; but when the lin^ht is defi- ^^^^ ^^^ tried. His attention was scarcely attracted by the high notes; but wheq 



cient, it dilates readily, in order to admit as great a number of rays as possible. "'^ '""^ °"^^ ^'^"'^ played, he brought his broad ears forward, remained evidently lis- 



Behind the pupil, a fluid in the shape of a double convex lens is placed, called the tening, and made use of sounds rather expressive of satisfaction than otherwise. The 



Crystalline humour, formed of denser materials than any other liquid in the human '^'^" ^""""^ °^ "'^ French horn produced the same effect. But the Lion was much 



Eye. The remaining portion is filled up with the Vitreous humour, which is the most ^""^ ^°''"^^y affected. When the high notes were played he remained silent and 



plentiful of all its fluids. The inside of the Sclerotica being lined with a coloured motionless, but listening with deep attention. No sooner, however, were the low 



Tiscid secretion called Pigmcntum nigrum, or black Pigment, and the inner surface ""'^^ sounded than he sprang up, endeavoured to break loose, lashed his tail, and ap- 



of the Iris, with a dark brown pigment, any scattered rays of li-rht which would other- peared to be enraged and furious, so much so, as to alarm the female spectator!. This 



wise render vision obscure are intercepted. These pigments are therefore of the "^ accompanied with the deepest yells, which ceased with the music. 



»ame utiUty with the black paint which Imes the interior of telescopes and other The Cranium, or skull of the Mammalia, may be subdivided into 



