To return then to the consideration of this.skuil... The disturbance of growth is entirely in the prechordal part of the cranium, and therefore particularly related to the nose and eyes. The initial lesion is a limited one, but its effects are far reaching. It must not be forgotten that while chondrification and ossification are proceeding in the base of the primitive cranium, and to a much greater extent during ossification of the membranedeveloped superstructure, skull-moulding is modified by the growing brain, and it is the telencephalon and the thalamencephalon which will be specially involved. That part of the brain which develops behind the dorsum sellæ, the mid-brain, the hind-brain, cerebellum, and pons, is not affected, at any rate not to any appreciable extent. The immediate result of the interference with the development of the ala temporalis is that the brain has not in that part sufficient room for expansion and it forces itself laterally. Interference with growth in the region of the pterion results, as is seen in oxycephaly and many other congenital deformities, in a retention of the great depth of the occipital chondrocranium which is found in the embryo,13 and this entails a vertical position of the supra-inial portions of the occipital bone and generally results in brachycephaly. In such circumstances no strain is thrown on the lambdoid suture, therefore no intersutural bones are developed. The want of backward development of the occiput, though not inconveniencing the cerebellum or posterior lobes, gives the growing brain a forward impetus. As a result of shortcomings in the formation of the bones and increased lateral cerebral pressure numerous and large intersutural bones have formed at the asterion and pterion, and perhaps flattening or opening out of the fissures of Sylvius may have determined the unusual thickness of the posterior borders of the smaller sphenoidal wings.

As far as the brain is concerned the interference with its backward and lateral expansion has thrown the stress chiefly on the prosencephalon. Posterior to this the growth of the great ganglia of the brain-base has proceeded uninterruptedly and retention of their functions has been assured. Therefore the individual develops normal ambulatory powers, normal sensation, and is of sufficient physique; though one should not be surprised to find a disturbance of the tectal autonomic centres which might find expression in want of full somatic growth and in the presence of acrocyanosis. But anterior to the dorsum sellæ, deformation of the brain and the pressure on

it have interfered with the development of the higher cerebral functions. In the growth of the pallium and neopallium the nerve cells or the grouping of them have been interfered with, or the complicated system of connecting tracts between the higher ganglia or even between the two cerebral hemispheres may have been interrupted or imperfectly evolved. The result would be imbecility, using that term as intermediate between idiocy and a higher grade of mental deficiency. The initial defect in the skull which I have described has fully developed in the embryo by the third month but the great pallial growth only commences then. The volume and bulk of the brain has been but little interfered with though the functions have been materially affected.

At an early period of embryonic life, even at the sixth week, the anterior cerebral vesicles bulge from the front part of the prosencephalon, while the fronto-nasal process forms a broad belt of tissue at a lower level in the middle line. At this time too the chondro-cranium forms, and as soon as the abnormal smallness of the ala temporalis makes itself felt pressure will be produced anteriorly. The subsequent want of room for lateral expansion and the continuing pressure from behind would account for the retention of the fœtal facies. Some moulding of the chondro-cranium would take place, and the jugum sphenoidale be rendered or remain concave from side. to side. For the same reason the tuberculum sellæ would be poorly developed, and the sulcus chiasmatis would not assume a backward direction but remain directed upwards, as also would the internal openings of the optic foramina. The pressure which renders or keeps concave this portion of the sphenoid must act even more decidedly further forward, and the horizontal plate of the ethmoid, that is the cribriform laminæ, would form a concavity and be extended in all direc. tions but particularly in breadth. Undoubtedly a strain occurs at the junction of these bones and this strain would be bilateral and symmetrical, and so in the spheno-ethmoidal suture, in the spheno-frontal suture, and in the fronto-ethmoidal suture, there is a symmetrical development of intersutural bones. But another peculiar result has been produced, namely, that in the spreading out of the cartilaginous nasal capsule, or by a centrifugal increase in size during ossification, the formative material of the ethmoid is used up in the abnormal size of the cribriform laminæ, and there have come into being neither

cristi galli nor ethmoidal labyrinths. Finally the concavation and broadening of the spheno-ethmoidal cerebral surface could not have occurred without traction, and this would tilt upwards the anterior portion of the nasal capsule and bring about the vertical axis of the nasal bones sagittally; while the orbits retaining their foetal lateral deviation would, by traction in the horizontal plane, ensure nasal bones of an unusual breadth and a strain which would produce in the internasal suture an intersutural bone.

The importance of the sphenoidal bone and its relation to cerebral development is nothing new. Three-quarters of a century ago, albeit more than ten years after the debacle, my illustrious predecessor, our first Conservator, Dr Knox,12 noted its value and briefly referred to the skull of an adult male congenital imbecile in which a sphenoidal deficiency was the sole osseous peculiarity. Under Sir John Struthers' ægis I feel I am following worthy footsteps.

It may be asked: Why add a new name, another variety, to the already copious varieties of cranial deformities? Can not hypertelorism be classed under one of the recognised varieties? The answer is: It can not. Hypertelorism is an entity having a definite origin, a definite course. It is dependent on a growthdisturbance of a minute portion of the embryonic cranial tissue, from which consecutively certain deformities are produced. The deformities may vary in degree according to the degree of primary defect, but they are otherwise definite and fixed, and nothing else can simulate them, and the combination can only be caused by this one lesion for which the fortunate acquisition of this skull has enabled me to submit an explanation.

Addendum.

As the title of this lecture infers, I am unaware of any description of hypertelorism as an entity or even as a leading feature, and I do not know of any published description of a similar skull. Perhaps the following may not be irrelevant.

In 1890, as a variety of plagiocephaly, Fridolin 14 described the skull of a boy aged 3 months. It was asymmetrical, high and short, and the right side flatter than the left. The frontal and parietal eminences were absent from the right side, and the upper two-thirds of the right half of the coronal suture were synostosed. In my opinion the partial synostosis and the absence of the right parietal and frontal eminences are related.

to each other, the synostosis having prevented their development, and, an unwonted strain being thrown on the anterior fontanelle, a large intersutural bone has been the result. This part of the deformity is not uncommon, and has no particular relation to hypertelorism, but the other part of the deformity present has; and the presence of two defects in the skull need excite surprise no more than the coexistence or multiplicity of congenital defects elsewhere.

The right orbital cavity is higher and narrower than the left, and the distance between the eyes is in consequence increased. The right orbital index is 155, the left is 84. In the right temporal region the great wing of the sphenoid is much narrower than in the left, the measurements being respectively 3 mm. and II mm. The right zygomatic bone is higher than the left, and the zygomatic arch is shorter. The right side of the root of the nose is 54 mm. from the acoustic meatus, the left is 69 mm. from the corresponding point on the left side. The right zygomatico-maxillary suture is partly synostosed; the infra-orbital suture is still open. The right nasal bone is absent; the left is very broad and extends to the right over the middle line; it measures at its root 9 mm. The nasal process of the right intermaxillary bone to which the inferior concha articulates by its anterior extremity is separated from the maxilla by a fissure 3 mm. deep-the sutura intermaxillaris facialis. A fissure still separates the two intermaxillary bones. The interpalatal suture inclines to the left, and the long axis of the foramen magnum to the right. The lower root of the smaller wing of the sphenoid is absent from the right side, so that the optic foramen is not closed up, and on the same side the anterior and middle clinoid processes are synostosed. There is no left middle clinoid process which of course is normal for an infant of this age. The right side of the mandible is less developed than the left, a derangement partly developmental and partly due to imperfect musculature which would accompany the right-sided osseous defect.

It is obvious that synostosis of part of the right side of the coronal suture could not explain all these defects which are entirely unilateral. It is not difficult from what we have seen in hypertelorism to visualise the right side of the skull Fridolin so minutely describes. Further, if one can imagine the deformity as bilateral, the similarity to hypertelorism will be at once

Is it not that the two nasal bones are fused?

recognised and the fault ascribed to the sphenoid, especially that portion of its greater wings which is developed in cartilage. The explanation I have given of hypertelorism makes a unilateral affection not only possible but probable.

In the osteoclastic activity which has resulted in so great alveolar absorption there is probably nothing to wonder at. A septic periodontitis, in a mentally-deficient person, incapable of being taught dental hygiene and nourished for the most part on soft, digestible, and easily-swallowed food, is certain to tend towards an osteoporosis rather than to provoke an osteoblastic reaction. There is other evidence, for example, in the osseous walls of the acoustic meatus and at the apex of each petrous bone, of unstable osseous tissue and perhaps in the imperfectlydeveloped brain cerebral control of osseous growth may have been abnormal.

Maggi 15 and Waldeyer 16 found the cranio-pharyngeal canal present in 40 per cent. of anthropoid apes, and it has been demonstrated by other investigators as present in rabbits, cats, and other animals with considerable frequency. It would be surprising if it were not occasionally found in the human subject, and in most text-books of human anatomy the occasional existence of a patent cranio-pharyngeal canal is referred to.

It is common to find in a full-time foetus or in the newlyborn child the site of either end of the cranio-pharyngeal canal indicated by a blind canal or by a funnel-shaped impression in the bone. Statistics of frequency vary much in accordance with the age of the skulls examined, and it is significant that the occurrence of a patent cranio-pharyngeal canal diminishes with age. Some facts as to its persistence have been usefully collated by Haberfeld.17 Landzert,18 who was the originator of the name "cranio-pharyngeal canal," says he found a complete canal present in 10 per cent., and Le Double 19 in 9 per cent. of newly-born children. If the numbers of the skulls examined by the authors quoted by Haberfeld be added together, excluding Le Double's observation of 100 skulls under 3 months of age, a complete cranio-pharyngeal canal is found twenty-nine times in 6281 skulls, or in rather less than 0.5 per cent. of presumably otherwise normal crania of all ages. As regards sex incidence opinions differ. Le Double found the canal present eighteen times, of which II were males, while Casselli, in a much more extended investigation, found it present twelve times, of which only 3 were males. The remains of the cranio-pharyngeal