W. E. Le Gros Clark

THE PROJECTION OF THE OLFACTORY EPITHELIUM ON THE OLFACTORY BULB IN THE RABBIT

In a previous study (Le Gros Clark and Warwick, 1946) the degeneration of olfactory receptors in the rabbit following complete or partial ablation of the olfactory bulb was examined by reference to sections of the mucosa covering the septal cartilage, stained by Bodians protargol method. Evidence was advanced to show that this is a true secondary degeneration following interruption of the primary olfactory neurons, and not the result of other factors such as vascular disturbance. It was found that the degeneration of the olfactory receptors occurs with great rapidity, for they undergo almost complete disintegration one week after removal of the bulb. The atrophy of the receptors is associated with a shrinkage in depth of the whole epithelium. The histological picture of the septal epithelium following partial lesions of the bulb incidentally led to the conclusion that there is no definite localized projection of different areas of the olfactory epithelium on to the bulb, for such lesions appeared to lead to a general thinning out of the receptors rather than to localized areas of complete degeneration. Later, evidence was brought forward by Adrian (1950), on the basis of electrophysiological studies, that there is in fact some degree of localized projection, though of a rather diffuse kind. He further made the interesting suggestion that this may have some importance as a basis for olfactory discrimination. It therefore appeared desirable to investigate the problem further by experimental anatomical methods, without limiting observations to a restricted area of the septal mucosa. As will be seen, this more extended enquiry has provided definite evidence of a general type of localization in the projection of the olfactory epithelium on the olfactory bulb.

THE PATTERN OF OLFACTORY INNERVATION

IT is desirable that, from time to time, commonly accepted statements regarding anatomical pathways and connexions in the peripheral and central nervous systems should be carefully reviewed in the light of modern technical methods of investigation, for it must be admitted that not a few of these statements are based on old methods which are now recognized to be too crude to permit of really accurate conclusions. In recent years, indeed, a number of apparently well-established facts have been shown by critical studies to be erroneous. For example, the so-called ventral nucleus of the lateral geniculate body and the pulvinar are no longer accepted as terminal stations of the optic tract, and the strie acoustice have been shown to be unconnected with the auditory system. Of all the systems in the brain which call for a careful revision, that related to olfaction seems most urgently in need of treatment. The complexities of the rhinencephalon, as they are expounded in most text-books, are largely based on the accounts of early investigators who had to rely for their conclusions on the examination of Weigert sections of normal material or of Marchi preparations-methods which, as is now well recognized, are both highly unreliable by themselves even for fibre connexions of an apparently simple and direct kind. There is reason to think, indeed, that some components of the so-called rhinencephalon should be excluded altogether from this system. Thus, there is now grave doubt whether the hippocampus (together with its direct and indirect connexions, such as the mamillary body and the anterior nucleus of the thalamus) can in any way be said to be primarily concerned with smell. In view of these uncertainties, it was decided to investigate anew the olfactory connexions of the brain, and in this paper we are concerned with the pattern of innervation of the olfactory mucosa, and with the projection of the latter on the olfactory bulb. Our main intention was to approach these problems by studying the retrograde degeneration in the olfactory epithelium which follows partial or total destruction of the olfactory bulb. In the course of the investigation, material was also obtained which permitted certain observations to be made on the olfactory receptors, on the cytological details of their retrograde degeneration, and on the intranasal course of the olfactory nerves. Methods

PALAEONTOLOGICAL EVIDENCE BEARING ON HUMAN EVOLUTION

Palaeontological evidence bearing on the evolutionary origin of the Hominidae is provided by dryopithecine fossils of Miocene and Pliocene date. These fossils consist almost entirely of jaws and teeth. They indicate that, while the dentition of Dyropithecus was essentially simian in its general characters, in certain features, notably the cusp‐pattern and proportions of the molars, it showed some significant approach to a human type of dentition. In certain allied genera, this approach is still further emphasized by the conformation of the dental arcade. The fact that in some species of these fossil apes the characteristic specializations of modem anthropoid apes were already evident in incipient form suggests that the divergence of the evolutionary line leading to the Hominidae from that which culminated in the modem genera of anthropoid apes must probably be referred to the beginning of Miocene times.

THE SCOPE OF TEACHING AND RESEARCH IN ANATOMY

Anatomy is the science of the form and structure of living organisms. That is to say, it is concerned with the study and interpretation of those factors which determine or modify form and structure, whether they are chemical, physical, physiological, developmental, or phylogenetic, and with the -precise relation between structure and function. It is clear, therefore, that the science of anatomy is very comprehensive in the scope of its inquiry. It is necessary to emphasize this for the reason that, in this country at least, anatomy seems to be regarded by many workers in the cognate sciences as rather a limited subject. If this is the case, the fault is to be found not in the science of anatomy itself, but rather in its accredited exponents.

Progress and trends in the science of anatomy.

I well recollect, at the International Anatomical Congress held 20 years ago at Amsterdam, hearing that distinguished anatomist the late Professor C. U. Ariens Kappers deliver a notable presidential address of welcome. In the course of his address, without any hesitation and with perfect fluency, he changed about from one language to another, speaking as easily in Dutch, French, English, German, and Italian. I fear I am quite unable to emulate such remarkable linguistic ability in welcoming the delegates of the International Anatomical Congress now meeting at Oxford, and I am therefore limited to addressing you in my own language.