for which they are intended, were not present; and he may therefore be surprised to hear, that the only one which was altogether deficient was the olfactory; and the brain, with the exception of the greater part of the anterior lobes being wanting, was normal. Now Tiedemann tells us that such is very nearly the natural state of parts in a three months' embryo, every part of the brain being formed then, except the anterior lobes, and all the cerebral nerves, except the olfactory, being present. We have already adduced facts to shew that the absence of any organ does not necessarily suppose the entire absence of the nerves intended for its use. The converse of this state is also occasionally met with; the eyes, for example, are found, and yet there are no traces of retinæ or of optic nerves. Dr. Seiler mentions the case of a hydrocephalic child, which he examined; the sheaths of the optic nerves did not contain any medullary fibres, and they were so thin and delicate, that they could scarcely be traced on to the eyeballs; and yet these organs exhibited all their component structures, with the exception of their retina and corpora vitrea; and again, in a microphthalmous fœtus, no optic nerves could be discovered, and yet considerable advances in the developement of the eye had taken place. In like manner, the olfactory organs are sometimes found to be tolerably well-formed, while the olfactory, and even also the trigemini nerves have been wanting.

There still remains another important theme of reflection suggested by the consideration of the preceding malformations. We have seen that when the eyeballs are awanting, many of the accessory appendages of these organs, such as the lachrymal glands, puncta, and canals, are also not unfrequently absent, just in the same manner as we find that, when there are no testicles, the scrotum, prostate, and so forth, are either not at all, or only imperfectly developed. But we are not to allow ourselves to conclude from such occasional occurrences that there must be therefore a law or invariable operation of the organizing power, by which one part is formed in consequence of another part, or by which the different organs are evolved from the centre to the periphery. This has been a favourite speculation of some late anatomists; but most assuredly it is contradicted by the best ascertained results of embryology. The position laid down by Rudolphi is much more correct;"that every part of the centre and of the periphery is formed after its own definite and distinguishing type, according to the period of its developement, and either primarily in its own locality, or to be subsequently affected by time or by situation, provided all along that no impediment or arrest ever take place." This holds true, in an especial manner, with the developement of the nervous system. Klinkosch found, in a case where onc of the trunks of the trigeminus was entirely deficient, its peripheral ramifications in their proper localities; and Dr. Seiler adduces his own observations in proof of the accuracy of the statement. He examined a fœtus, in which, as in the example related by Rudolphi, all the nerves were present, although the brain and the spinal marrow were altogether awanting. In consequence of a few of such cases, M. Serres, in his work on the Comparative Anatomy of the Brain, published at Paris in 1824, announced the doctrine that the developement of the nerves commences at the periphery, and proceeds to a central point, at which all meet; but the whole history of embryology, from the first month until the perfect formation of all its organs, the earlier formation of the trunk, the subsequent formation of the

head, and of the extremities, (these two shooting from the centre peripherally) and lastly every instance of regeneration stand opposed to M. Serres' hypothesis. The tendency of the developing power is always from the centre towards the periphery; parts which are intermediate may indeed be arrested in their formation, while the parts on either side may advance in their normal progress; it is in this way that we explain the rationale of those cases in which the branches of a nerve are developed, while the trunk of the nerve is awanting, or in which the rudiments of the forearm and hand are found attached to the shoulder-blade, while the upper arm is altogether absent. Other examples illustrative of the same doctrine may be adduced from the occasional occurrence of a trunkless head superimposed upon another head; or of a bicephalous monster, or of the complete absence of the cervical vertebræ, the head being then joined on to the dorsal vertebræ, &c. and still more striking proofs are those strange anomalies of organization, in which one quarter, or even one entire half of the body is deficient, as for example, the head, chest, and part of the belly, while the other quarter, or other half is regularly formed. Surely such monstrosities are quite irreconcileable with Serres' doctrine of concentric or converging develop

ment.

PART II.-OF THE ORIGINAL MALFORMATIONS OF SPECIAL OR INDIVIDUAL PARTS OF THE EYE.

Orbits. In the preceding part of this paper we have spoken of most of the congenital defects of these cavities. Whenever the head is much enlarged by hydrocephalus at birth, it has been found that the orbitar plates of the frontal bone have generally their oblique, or nearly horizontal position altered to a more perpendicular plane, and that thus the size of the orbits is necessarily reduced. If again the development of the olfactory organs be imperfect, or irregular, the situation and shape of the orbits may be affected in consequence; thus they may be placed too close to each other, or they may be even melted into one, constituting the monophthalmus cyclopicus. A variety of other malformations is occasionally met with; but the consideration of these need not detain us longer It is important to observe that in many cases of microcephalus the orbits are not only proportionally too small, but they even want one or more of their component bones.

Eyelids. The shortness of the lids, when they are insufficient to cover the globes entirely (lagophthalmus), may very often be referred to an interruption of the development of these parts. Sometimes the lids are altogether awanting, although the eyeballs be perfect. Morgagni alludes to his having seen a specimen of this deformity in a man whose corresponding eye was quite destroyed; but he does not mention whether this was congenital or not. The deficiency of the lids in anophthalmous monsters is by no means infrequent. The adhesion of the eyelids to each other (anchyloblepharon) or to the conjunctiva of the ball, (symblepharon) is probably oftener the effect of an intra-uterine inflammation, than of any original malformation. That inflammation of different organs of the foetus do occasionally take place, we can have no rational doubt, when we consider the numerous instances on record, authenticated by good witnesses. Chaussier found in

a seven month fœtus most distinct traces of enteritis and diaphragmitis. Vernan mentions having seen in the body of a new-born child a quantity of sero-purulent effusion within the pleure, which were at the time coated with lymph. The thymus has been found inflamed, and Otto in his Manual of Pathological Anatomy says that he has seen several well-formed and very obvious ulcerations on the lips and gums of a new-born infant. The conjunctiva oculi, in cases of congenital deficiency of the lids, has been noticed by several observers to have become thick and red; and this change is sometimes so striking, that the membrane has assumed the appearance of the membrana nictitans of birds.

It cannot then be questioned that the eyes, or some parts of them may become involved in disease, while the foetus is in utero; and it will sometimes require a practised observer to determine whether the abnormal appearances of the organ at birth are to be attributed to disease, or to a primitive malformation. Ectropium and entropium occasionally occur as congenital maladies; and also blepharoptosis, in which the upper eyelid from its unusual length hangs down over the lower one. In cyclopic monsters, there are sometimes rudiments of the four lids placed round the single eye; at other times there are none at all.

Lachrymal Organs. In our account of anophthalamus, it may have been observed, that there is no steady rule with regard to the presence or absence of these organs in cases of this congenital defect. In Klinkosch's case, they were awanting; but not so in that related by Rudolphi; and in an example which occurred to Weidele, the lachrymal gland was found lying in the place of the absent eyeball. Again, the lachrymatory apparatus may be either entirely or partially deficient, although the eye has been formed.

Cyclopic monsters very often present rudiments of the double formation of many of the ocular appendages; and among these, of the lachrymal gland.

Muscles of the Eyeball. It would be very interesting if we were better informed respecting the congenital malformations of these muscles, as probably considerable light would thereby be thrown on some of the causes of squinting (strabismus and luscitas). Wrisberg found in a man who had squinted greatly, the cornea to be higher up than natural, one of the recti muscles wanting, and the others to be grown together. Otto mentions the occasional shortening or even entire absence of some of the recti muscles in such cases. Dr. Seiler states that he dissected a case in which the two oblique muscles were wanting, although the eyeball and other parts were normal. Sometimes, but very rarely, more than the usual number of ocular muscles have been found. Kulmus and Meckel have met with two upper oblique muscles, which had separate origins and separate pullies, and Caldani has described a muscle which arose from the lower edge of the orbit and expanded itself on the lower lid.

The duplicity of the muscles is very common in cyclopia.

Nerves. Our notice of this head need be short, in consequence of our having repeatedly throughout this paper alluded to the condition of the ocular nerves in malformations of the eyeball. We have seen that some

or all of them may be either entirely wanting or that they may be reduced to mere membranous cords, having no medullary substance within. An interesting irrregularity is occasionally met with; viz. where the optic nerves run apart from each other throughout their whole course, from the thalami to the eyeballs: now, although such an arrangement has not hitherto been shewn by any anatomist to be normal at any stage of embryotic life, it points to a defect of the organising principle in joining the two lateral halves of the body. Numerous instances are on record in which this malformation was found, and yet the brain and adjacent parts were otherwise quite regular. It is by no means infrequently observed in microcephalous monsters. In a cyclopic dog-pup, Majendie could find no trace whatever of any optic nerve; the brain was exceedingly small, without any convolutions, and lay like a simple tubercle in the back part of the cranium. The first five pairs of cerebral nerves were quite wanting. A very similar case is related in Haller's lesser works. The converse of such occurrences is also sometimes met with; the eyeball being absent, while the optic nerve has been normally formed. This nerve, like most other parts of the eye, is usually, but not always, double in cyclopic monsters; and in such cases an irregularity of the entrance of the nerve or nerves is not uncommon.

Sclerotica and Cornea. The former of these membranes is, in the young fœtus, and even in children at the birth, very thin, and of a blueish-white colour; and if from any cause the perfect developement of the eye-ball has been impeded, this state of the sclerotic remains through life. In the third and fourth months of fœtal existence, the sclerotic is of an oval or lengthened shape, in consequence of its anterior part projecting very much forwards at these periods. This prominence (protuberantia scleroticæ fœtalis] becomes gradually less and less, so that by the ninth month it is not very apparent. In microphthalmous fœtuses it is generally most distinct. In them the cornea often remains cloudy, and not easily to be distinguished from the sclerotic; it has a lengthened shape, and appears to be surrounded with a purplish ring. Many of the congenital affections of this membrane which have been attributed to foetal disease, are in fact only signs of a retarded developement. Thus authors have often spoken of the cornea being found altogether awanting, the sclerotic being then continued over the front of the eye; probably this anomaly is always explicable on the above principle. In such cases it may almost always be observed that the supposed prolongation of the sclerotic is rather more thin and transparent than the rest of the membrane; and perhaps the most anterior or central point may be even moderately clear and permeable to the light. The example narrated by Kieser in Himly and Schmidt's Ophthalmological Dictionary seems to have been of this description. Dr. Farrar relates the cases of new-born triplets, in each of whom the cornea was quite opaque. In two the opacity had in a great measure disappeared within twelve months after birth; while in the third, no change had taken place at the date of the history, the child being at that time three years old. We must not however suppose that every case of congenital opacity of the cornea is referable to the cause now mentioned; for doubtless some are the effects of a previous inflammation in the part. Wardrop refers to several examples of congenital tumors growing on the cornea, and Baron Graefe has met with cases of telangiectasis,

or nævus of this membrane. A much more common malformation is the extreme or morbid prominence of its convexity, constituting the affection which has received so many appellations; such as "staphyloma corneæ pellucidum, or hyperkeratosis," by Himly; "ochlodes," by Taylor; "conicalformed cornea," by Wardrop; "sugar-loaf cornea," by other English surgeons; "cornée conique," "staphylome transparent de la cornée," by most French authors; and "kerato-conus," by Ammon. The most projecting point of the convexity is seldom at the centre of the cornea; but generally somewhat to the side; and often it has a peculiar glancing lustre, like a piece of polished glass; or it may have even an opalescent play of colours; or on the other hand it may be dull and smoky. This affection ought to be always distinguished from the other and more common variety of staphy loma [s. corneæ opacum]; also from hernia of the cornea [keratocele] and from dropsy of the eyeball. If the degree of the protrusion be not very great, the child may retain its vision, but must be exceedingly short-sighted; and unfortunately if it be considerable, the patients are almost always completely blind. To Professor Jager of Wurzburg, we are indebted for the best anatomical description of this malformation; it appears from his researches that the cornea is often unequally thick at different parts, being much thinner than usual in one place, and much thicker in another. Some of the other structures of the eye also are occasionally involved; thus the pupil may be closed, or the lens may be cataractous; or the retina amaurotic. Ammon and Jager have remarked that this congenital affection of the cornea is very often associated with some peculiarity in the formation or shape of the cranium; for in some it was unusually small and conical; in others, the frontal bone was much flattened and depressed, while the parietal and occipital bones projected more than ordinarily. Now in connection with these facts it is most interesting to find that those able observers, Ammon and Gescheidt, have discovered hyperkeratosis in a two-month embryo; and the question therefore arises in our minds, whether the affection is to be viewed as the result of a retarded or interrupted developement, or of a fœtal disease. Wimmer inclines to the former opinion, and supports it by referring to the condition of the eye, not only in those animals which are lower in the scale, but also in the young of all mammals, including man ; the cornea being uniformly more conical during its foetal developement than it is afterwards. He 66 says, many physiologists have ascertained that the human embryo, from the period of its earliest to that of its perfect formation, gradually passes through several stages of organization, each succeeding one being of a higher grade than that which went before it.

Now in many animals, as in the genera astacus and lucanus, among insects; in most birds, especially in those which are carnivorous, and in some of the mammiferous class, as the mole and porcupine, a very great convexity of the cornea is the normal or healthy state."

But this merely analogical reasoning cannot be admitted as sufficient to resolve our doubts; and until it has been proved by competent authorities that the natural condition of the embryotic cornea is that of extreme prominence, we must hesitate before we arrive at any conclusion. Hitherto embryologists have not succeeded in determining this point: and if the weight of their testimony leans to any side, most assuredly it is unfavourable to Wimmer's view of the question. The observation therefore of Ammon and