proportions which these different parts or chambers of the brain bear to one another. He supposes, also, that this organ is possessed of two distinct sets of nervous fibres-a secernent and an absorbent; both directly connected with what is called the cineritious or ash-coloured part of the brain; the former issuing from it and secreting the fluid of the will, or that by which the mind operates on the muscles; and the latter terminating in it, and conveying to it the fluid of the external senses, secreted by those senses themselves, and communicating a knowledge of the presence and degree of power of external objects. This elaborate theory, and the facts to which it appeals, were very minutely investigated, a few years ago, by a very excellent committee of the physical class of the French National Institute, assisted by Dr. Spurzheim, the intimate friend and coadjutor of its inventor, and who is well known to have contributed quite as much to the establishment of this speculation as himself. This committee, after a very minute and cautious research, gave it as a part of their report, that the doctrine of the origin and action of the nerves is probably correct; but that this doctrine does not appear to have any immediate or necessary connection with that part of Dr. Gall's theory which relates to distinct functions possessed by distinct parts of the brain.* The origin, and distribution,

and action, however, of the nervous trunks have since been far more accurately traced out by Sir Charles Bell, M. Magendie, and various other

* For an examination of the general subject of craniology and physiognomy, see Vol. III. Ser. 111. Lect. xIII.

physiologists; while, in refutation of the doctrine that ascribes distinct functions to distinct parts of the brain, it may be sufficient to observe, for the present, that many of the nerves productive of different functions originate in the same part, while others, productive of the same function, originate in different parts.

There is no animal whose brain is a precise counterpart to that of man; and it has hence been conceived, that by attending to the distinctions between the human brain and that of other animals, we might be able to account for their different degrees of intelligence. But the varieties are so numerous, and the parts which are deficient in one animal are found connected with such new combinations, modifications, and deficiencies in others, that it is impossible for us to avail ourselves of any such diversities. Aristotle endeavoured to establish a distinction by laying it down as a maxim, that man has the largest brain of all animals in proportion to the size of his body; a maxim which has been almost universally received from his own time to the present period. But it has of late years, and upon a more extensive cultivation of comparative anatomy, been found to fail in various instances: for while the brain of several species of the ape kind bears as large a proportion to the body as that of man, the brain of several kinds of birds bears a proportion still larger. M. Sömmering has carried the comparison through a great diversity of genera and species: but the following brief table will be sufficient for the present purpose. The weight of the brain to that of the body, forms,

M. Sömmering has hence endeavoured to correct the rule of Aristotle by a modification, under which it appears to hold universally; and thus corrected, it runs as follows: "Man has the largest brain of all animals in proportion to the general mass of nerves that issue from it."

Thus, the brain of the horse gives only half the weight of that of a man, but the nerves it sends forth are ten times as bulky. The largest brain which M. Sömmering ever dissected in the horse-tribe weighed only 1 lb. 4 oz., while the smallest he ever met with in an adult man was 2 lb. 5 oz.*

It is a singular circumstance, that in the small heart-shaped pulpy substance of the human brain, denominated the pineal gland, and which Des Cartes regarded as the seat of the soul, a collection of sandy matter should invariably be found after the first few years of existence; and it is still more singular, that such matter has rarely, if ever, been detected but in the brain of a few bisulcated animals, as that of the fallow-deer, in which it has

*Stud. of Med. iv. 11. 2d edit.

been found by Sömmering*; and that of the goat, in which it has been traced by Malacarne.+

The nervous system of all the vertebral or first four classes of animals,. mammals, birds, amphibials, and fishes,-are characterised by the two following properties: first, the organ of sense consists of a gland or ganglion with a long and bifid chord or spinal marrow descending from it, of a smaller diameter than the gland itself; and, secondly, both are severally enclosed in a bony case or covering.

In man, as we have already observed, this gland, or ganglion, is (with a few exceptions) larger than in any other animal, in proportion to the size of the body; without any exception whatever in proportion to the size of the chord or spinal marrow that issues from it.

In other animals, even of the vertebral classes, or those immediately before us, we meet with every variety of proportion; from the ape, which, in this respect, approaches nearest to that of man, to tortoises and fishes, in which the brain or ganglion does not much exceed the diameter of the spinal marrow itself.

It is not therefore to be wondered at that animals of a still lower description should exhibit proofs of a nervous chord or spinal marrow, without a superior gland or brain of any kind; and that this chord should even be destitute of its common bony

Dissertatio de basi Encephali, 1778, and Tabula baseos Encephali, 1799. See Blumenb. p. 292.

+ Dissert. p. 10. See also Blumenbach, Anat. Comp.

§ 206.

defence. And such is actually the conformation of the nervous system in insects, and, for the most part, in worms; neither of which are possessed of a cranium or spine, and in none of which we are able to trace more than a slight enlargement of the superior part of the nervous chord, or spinal marrow, as it is called in other animals, a part situated near the mouth, and apparently intended to correspond with the organ of a brain. The nervous chord, however, in these animals, is, for the most part, proportionally larger than in those of a superior rank; and at various distances is possessed of little knots or ganglions, from which fresh ramifications of nerves shoot forth, like branches from the trunk of a tree, and which may perhaps be regarded as so many distinct cerebels or little brains.

In zoophytic worms, we can scarcely trace any distinction of structure, and are totally unable to recognise a nervous system of any kind. The common and almost transparent hydra or polype, which is often to be found in the stagnant waters of our own country, with a body about an inch long, and arms or tentacles in proportion, appears to consist, when examined by the best glasses, of nothing but a granular structure, something like boiled sago, connected by a gelatinous substance into a definite form. * Hydatids and infusory animals exhibit a similarity of make. The common formative principle of all these may be reasonably conjectured to consist in the living power of the blood alone, or rather of the fluid which answers the purpose of blood; and their principles of action to be little more than instinctive.

* Blumenb. Anat. Comp. § 203.