JOURNAL OF COMPARATIVE NEUROLOGY. VOL. XIII. CHART 1.

THE BRAIN OF THE ARCHÆOCETI.1

By G. ELLIOT SMITH, M. A., M.D.,

Fellow of St. John's College, Cambridge; Professor of Anatomy, Egyptian Government School of Medicine, Cairo.

[A paper read before the Royal Society of London, February 12, 1903.]

So far as I have been able to ascertain, nothing whatever is known of the form of the brain or, more strictly, of the cranial cavity in the Archæoceti. Hence no apology is needed for presenting even this imperfect account of two cranial casts representative of this sub-order, which have come into my hands.

Among the Eocene remains found in the Fayûm region of the Egyptian desert by Mr. H. J. L. BEADNELL and Dr. CHARLES W. ANDREWS, in 1901, there was a broken skull of Zeuglodon, from which it was possible to obtain a mold, representing the form of the greater part of the dorsal and lateral aspects of the brain. A plaster cast was made in the British Museum at the instance of Dr. ANDREWS, who kindly placed it at my disposal for description.

In the following winter (1902), Mr. BEADNELL found in the same locality a natural cranial cast of the same size and general form as the artificial cast of Zeuglodon. It is obvious at a glance, if the two specimens be placed side by side, that the natural mold belongs to some member of the Archæoceti,

1 These notes were originally intended for the Report on the Survey of the Fayûm, to be issued by the Egyptian Survey Department, and are now published separately with the permission of the Under Secretary of State for Public Works and Captain H. G. LYONS, Director-General of the Survey Department.

' C. W. ANDREWS, "Extinct Vertebrates from Egypt," Part II. (Extracted from the 'Geological Magazine,' N. S., Decade IV, vol. 8, 1901, p. 437,Zeuglodon Osiris, Dames'.)

but whether to the same species or even genus as the other specimen must at present remain an open question.

Mr. BEADNELL kindly placed this specimen at my disposal. The size and relative proportions of the different parts are almost identical in the two casts. Nevertheless, there are a considerable number of differences, some features being displayed in one and not in the other, and vice versa. Many of these differences are obviously due to the imperfections of the casts, and especially to the failure of the plaster mold to represent the true form of the brain. But there are several peculiarities of the natural cast-such, for example, as the form of the caudal part of the cerebellum and the shape of the cerebral hemispheres which are difficult to reconcile with the artificial mold, even if we admit that the inner face of the cranium (from which the latter was made) is damaged or imperfectly cleaned. The differences, nevertheless, are sufficiently pronounced to indicate a generic distinction between the two specimens; and in this connection it is interesting to recall a statement made by Dr. ANDREWS in his first reference to Zeuglodon, as "including apparently DAMES' Z. Osiris, and perhaps a second species. It would, however, be very unwise, because it would serve no useful purpose, and possibly lead to error, to found a new genus or even a new species on the evidence of this natural cranial cast, when our source of information concerning the known genus (Zeuglodon) is as unsatisfactory as that obtainable from the artificial one about to be described. More especially so, when it is remembered that in the case of the only indisputable facts (i. e., size and general form) the two casts are agreed. I shall therefore merely describe and attempt to explain the meaning of the form of the two specimens, and leave the question of the specific identity open for future research.

The general appearance of the brain is extraordinarily peculiar (figs. I and 2). The shape of the anterior part of the natural cast (fig. 1, a and b) closely resembles the cerebrum of

1 'Geological Magazine,' September, 1901, p. 401.

a Lizard greatly magnified. An anterior prismatic stalk (a), representing the pedunculi olfactorii, suddenly expands into a plump, broad, smooth mass (b), showing the form of the chief part of the cerebrum. The maximum breadth of the two hemispheres (fig. 1, b) is 95 mm.; the greatest length of each (mea

Two-ninths

FIG. 1.-Dorsal aspect of the natural cast described in the text. natural size. a, olfactory peduncles; b, cerebral hemisphere; c, d, cerebellum; e, é, fragments of skull.

sured in front from the point where the ventral surface of the olfactory peduncles appear to expand into the chief mass of the hemisphere) is 47 mm.; and the maximum depth is 54 Each cerebral hemisphere (exclusive of the olfactory peduncle) is slightly broader than it is long.

mm.

The two olfactory peduncles are represented in the natural cast by a single prismatic process. This extends forward for a distance of 37 mm. (measured along the dorsal edge) in front of the point where the expansion to form the hemispheres com