minutest nerve, yet as regards the physiology and psychology, we are probably at the present time as we were at the commencement of the 17th century with respect to the circulation, at fault, waiting for some master-mind to elucidate the subject. Many of the parts of this system are still obscure in their meaning, though, no doubt, capable of being unravelled up to a certain point; the ultimate connexion of the spiritual with the material, of mind with brain. and nerve, and the dynamic action of one upon the other, will probably remain for ever a mystery.

The anatomy of the brain was not unknown to Galen, nor to Herophilus and Erasistratus, whom he quotes. Cassius saw the decussation in front of the medulla oblongata. The anatomists of the renaissance were not inactive. Achillinus, Stephens, Vidus Vidius, Columbus, and Eustachius, for instance. Varolius, Arantius, Lieutaud, Willis, Vicq d'Azyr,* and the Monros, have been labourers in the same field.

Most of the cerebral nerves were known even to Galen, but the olfactory from their softness appear to have been often overlooked. Stephens demonstrated several; the distribution of the trigemini, the vagus, and the phrenic, as well as the sympathetic. Fallopius and the acute Eustachius investigated the difficult neurology at the base of the cranium. Fallopius is said to have confounded the seventh and fifth. The slender patheticus was known to Achillinus, and Columbus distinguished in the orbit the third from the ocular portion of the trigemini. All the nerves, thanks to the patient investigation of Willis, Vieussens and Walther, as well as more recent or even living anatomists, have now been well traced.

The organs of sense have always obtained the attention of the anatomist, particularly that beautiful dioptric instrument, the eye. Beranger knew the minute lachrymal points situated at the inner corner of the eye, and the lachrymal

* Vicq d'Azyr's large work, with coloured plates, is principally descriptive of the cephalic circulation. It was dedicated to Louis XVI.

apparatus generally. The Arabs understand this part of anatomy to the present day, as well as the diseases of the eye in general. The curious pulley of the upper oblique muscle was known to Rondeletius and Fallopius. Vesalius figures the crystalline lens as a sphere, and as occupying the centre of the eye. The membrane closing the pupil in the foetus was discovered by Wachendorff, in 1740.

The ear is a complicated and curious organ, contained in its essential parts in a very small space. The semicircular canals and cochlea were known to the ancients; the little malleus and incus to Achillinus and Carpi, and the latter described the tympanum. The curious and minute bone, the stapes, was rather an important bone of contention between the three great men, Fallopius, Eustachius, and Ingrassias, who all met with it about the same time, as they were industriously unravelling the structure of this minute

organ.

We pass over the skeleton and muscles; the names of Cheselden, Monro, and Albinus, of Clopton Havers, and Duverney, and of Fernel, Winslow, Bidloo, Cowper, and Douglas may be connected with the bones, the structure of the same, and the muscles. Columbus, in opposition to Fallopius, denied vehemently the existence of the pyramidales muscles, taking the exception for the rule.

Thus we believe we have shown that, with a very few exceptions, human anatomy has been thoroughly investigated, and is therefore competent to throw all possible light on the art of medicine.

Human anatomy and physiology have often been as much advanced by the study of that of the lower animals as by that of man himself; and this still remains an inexhaustible field of discovery, notwithstanding a host of inquirers—a Hunter and an Owen in England, a Blumenbach, Carus, and Meckel in Germany, and a St. Hilaire and Cuvier in France.

Again, during the last twenty years, the minute structure of organic beings has been submitted to closer observation by means of the superior instruments of the present day.

However, perhaps, too sanguine an expectation is often entertained with respect to the microscope. Though a powerful lens reveals the minute structure of an organ or tissue, yet it often brings us little nearer the comprehension of its physiology-sensation, contractility, secretion, nutrition, or absorption. Dr. Holland observes,-" After the most exact researches of late years, we do but partially comprehend those minute and complex mechanisms by which, in spaces barely accessible to the nicest instruments, the various functions of absorption, secretion and exudation, as well as the translation of blood from arteries to veins, are all simultaneously going on." Still, much interesting matter has been elicited by the histologists-the beautiful structure of the kidney, above alluded to, and that of the liver also; the tissues and vessels of plants; the structure of cartilage, bone, tooth, muscle, cilia, cellular membrane, fat, and skin in animals; also that of morbid growths, deposits, and degenerations; the microscopic character of the blood and other fluids, and the organization and characters of parasitical beings. It would be invidious to endeavour to call over the muster-roll of this band of observers.*

* Amongst foreign writers, Vogel, Wagner, Mandl, Donné, Kölliker, Gruby, and Robin, have published beautifully illustrated works on these subiects.

KP WMor

CHAPTER II.

A review of the nervous system, and the present state of our knowledge of it-Its anatomy and physiology as found in the different classes of invertebrate animals-The spinal cord, and encephalon in vertebrata and in man-The cerebral, spinal, and ganglionic nerves-The physiology of the nervous system-Pathology.

THE nervous system is worthy of a lengthened consideration. Though its anatomy in man is well understood, yet we cannot say the same with regard to its functions, particularly as connected with the different parts. As yet no second Harvey has arisen to furnish us with the key to the

enigmas included in this part of our subject. It is, probably, to comparative anatomy that we must look for further light in this difficult inquiry.

Feeling, motion, digestion in a sac or stomach, and the evolution of young or ova, may exist in animals which have no apparent nervous system. We have in vain endeavoured to find one in the highly sensitive and contractile sea-anemone (Actinia), though Spix thought he did so. It is certainly difficult to perceive in the star-fish (Asterias), though Tiedemann is good authority for its presence there— disposed like the animal or starlike, with a ring around the mouth. (Pl. I. Fig. 1.)

When the organs of motion become more perfect, and sensation less diffused, there must be nerves and ganglia, the latter the seats of volition or motor impulse and perception; the former the conductors of such impulse from, and of the sensation to, the ganglionic sensorium; also to connect the actions of distant organs with each other.* But in the Ascaris (of the horse) (Fig. 2), the nervous system appears to be two distant parallel cords, with a few accessory filaments anteriorly, and, some say, a ring around the mouth. Siphunculas (Fig. 3), also an elongated animal, has only one long cord, with but slight appearance of ganglia upon it, giving branches anteriorly to the strong muscles of the proboscis, and others at regular intervals to the muscular integument. The last leads to the sea-mouse (Aphrodite, Fig. 6), where we have a distinct sensorial ganglion above the mouth, encompassing the commencement

* In animals which have no nerves or ganglia to combine the movements of the different contractile parts, such as tentacles, &c., we have not the consentaneous and rapid contractions of higher animals, but rather such gradual and continuous movements as we see in the sensitive plant. However, in these lower animals, in their cilia, for instance, in the spinal pedicle of the Vorticella, or in the exertile arms of the Beroe, we sometimes see very rapid movements, but perhaps of a peculiar nature, and not dependent either on the muscular or nervous tissue.

With such a nervous system as this, the movements, unlike those of the annelides, must be instantaneous.