large mammalian body, even if the cerebrum is small. I cannot offer any more satisfactory explanation of the magnitude of the cerebellum in Zeuglodon than this,

It is clear from the foregoing that the extraordinarily great contrast in the appearance of the brain of the Archæoceti and that of the Cetacea cannot be urged as a reason against their kinship, when it is remembered that the operation of known factors is quite sufficient to explain the transformation of the one type into the other in the time which has separated the Eocene period from the present.

Having disposed of these negative arguments, we may consider the positive evidence for Cetacean affinity in the brain of Zeuglodon.

The shape of the cerebrum, and especially its relatively great breadth, is peculiar. In fact, this form of hemisphere rarely or never occurs among mammals, other than the Cetacea. I have elsewhere' attempted to explain the shortness of the Cetacean hemispheres by the fact that the abortion of the basal (olfactory) parts of the cerebrum limits their longitudinal extension. This, however, is not the whole explanation, because in many microsmatic Sirenia (Halicore), and Pinnipedia (Otaria, Phoca), the hemispheres are not especially broad. The disproportionate breadth seems, in fact, to be to some extent a characteristic of the Cetacea; and, in this respect, Zeuglodon agrees with them.

The peculiar elongation of the olfactory peduncles beyond the anterior extremities of the hemispheres is rarely found in mammals, though it is common enough in Reptiles and the Ichthyopsida. In fact, the exact parallel to the condition found in Zeuglodon occurs among recent mammals only in the Cetacea.2 An analogous condition is found in the extinct Lemuroid Megaladapis [described by FORSYTH MAJOR (op. cit.)] and some Amblyopoda.

1 'Catalogue of the College of Surgeons,' op. cit., p. 350.

2 Full references to this are given by FORSYTH MAJOR, "On the Brains of Two Sub-Fossil Malagasy Lemuroids," 'Roy. Soc. Proc.' vol. 62, 1897, p. 48, second footnote.

...It is not without interest to note that the two outstanding features of the cerebral hemispheres of the Archæoceti, even if their value as indices of kinship be slight, both find their near, est parallel in. Cetacea. There are no characters of the brain of the modern Cetacea which can be regarded as certainly distinctive, if we put aside such features as the extreme dwindling of the olfactory apparatus, and the enormous development of the neopallium. Both must be regarded as late acquisitions, not to be expected in an Eocene mammal. Under these circumstances these slight points of positive evidence of the relaţ tionship of the Archæoceti and Cetacea must be allowed some value, as reinforcing the testimony of the skeletal parts...tay na If we seek to institute closer comparisons between the brain of Zeuglodon and of the Qdontoceti and Mystacoceti with a view to the determination of its relationships, we are not unnaturally doomed to disappointment. It might, perhaps, be supposed by some anatomists, that the absence of an olfactory bulb in the Odontoceti might point to a closer affinity of Zeuglodon to the Mystacoceti, in which a small olfactory appa¬ ratus is retained. But there is every indication that the ol, factory apparatus of the Odontoceti has become aborted quite recently,, !! harma zin q25 to 994 295

1

1

FIG. 3.-Ventral aspect of brain of an early fœtus of Monodon. Natural size. a. d., locus perforatus (area desert); b.o., bulbus olfactorius; Ap, lobus pyriformis.

Thus in a specimen of the embryonic brain of the Narwhal Monodon), which was given to me some years ago by Professor. Howes, the remains of the olfactory bulb (fig. 3, 6,0.) are still

quite visible as a small umbilicate area in part of the desert region of BROCA (6g. 3, a.de), wherefore it follows that in the early embryo, the olfactory bulb and peduncle develop as in all other mammals. Moreover, in all Odontoceti, traces of the pyr riform labe, are found even in the adult and in the brain of Kogia greyi the rhinal fissure and the typical (macroscopically only) pyriform lobe, are retained in a form as clearly defined as that of any macrosmatic mammal (fig. 4) Professor HASWELL, in, describing this brain emphasises the fact that the most, reripidiconq bas) vinist,

B: 5 db ti

FIG. 4.-Ventral aspect of left hemisphere of Cogia greyi. Reduced approxi mately one-half. a.d., corpus striatum (area desert); b.o., place occupied by bulbus olfactorius in foetus; f.r.a., fissura rhinalis anterior; f.r.p., fissura rhinalis posterior; .p., lobus pyriformis.

markable feature of the [basal] region, and perhaps of the whole brain, is in the great depth of the ectorhinal fissure, a feature marking off the present form very strongly from Delphinus" (p. 438). Since his illustrations do not properly delineate this interesting conformation, Professor HASWELL

1 W. A. HASWELL, "On the Brain of Grey's Whale (Kogia greyi)," 'Linnean Society of New South Wales Proc.,' vol. 8, 1883 (publ. 1884), pp. 437-439, pl. XXI.

kindly permitted me to examine his specimen; and Mr. J. P. HILL has made me an excellent photograph (of its ventral surface), roughly reproduced the accompanying drawing (fig. 4). It shows the complete and quite-typical rhinal fissure and the characteristic pyriform lobe. In its anterior part the rhinal

fissure is fully a centimeter deep.

The exact reproduction of these characters of the rhinencephalon in an adult anosmatic Cetacean, and the presence of the olfactory bulb in the foetal Narwhal, show that these toothed Cetaceans were certainly (and probably quite recently) derived from ancestors presenting the normal mammalian type of olfactory apparatus. The absence of the olfactory bulb and peduncle in the Odontoceti cannot, therefore, be considered a just reason for adopting the utterly improbable suggestion of a nearer affinity of the Archæoceti to the Mystacoceti than to the Odontoceti.

Estimated by the amount of sand which it displaced, the bulk of the natural cast (including that of a considerable quantity of matrix attached to the base of the brain and some small fragments of bone) is 410 c. c. If the necessary corrections and estimations be made from this gross cubic capacity, the weight of the brain in the Archæoceti must have been considerably less than 400 grammes, and perhaps nearer 300, as against that of the recent Cetacea, which ranges from 455 grammes in Kogia (HASWELL) to 4,700 grammes in Balanoptera (GULDBERG).

LITERARY NOTICES.

Functional Changes in the Dendrites of Cortical Neurones.'

This paper is largely a reprint of a work published in 1897 in the first volume of the Travaux de l'Institut Solvay, whose results the author now regards as fully confirmed and established. Some of these conclusions are as follows:

The pyriform appendages (spines or thorns) of the dendrites of the cortical neurones constitute the terminal apparatus of the dendrites; they increase considerably the surfaces of the nerve cells and play an important rôle in the physiology of the brain, for in the case of severe disturbance the appendages disappear partially or wholly from the affected cells.

Varicosities represent in the adult brain pathological modifications of the nerve cell. They appear abundantly only in course of grave disorders and are rare in the brain of the healthy animal. In the normal adult the dendrites of cortical neurones do not show varicosities, but are thickly set with the pyriform appendages.

In prolonged etherization, or electrical stimulation or fatigue of the cortex the pyriform appendages disappear, while varicosities are present, but these two phenomena are really independent of each other and the appendages may disappear without any trace of varicosities making its appearance. The author concludes from the disappearance of the appendages that these are motile, but is unable to determine the mechanism of their movement. The cortex is never uniformly involved in the reactions to fatigue, etherization, etc., but beside the affected areas are others apparently unaffected. The paper is followed by a list of 14 titles of papers by the same author on related subjects. C. J. H.

1 STEFANOWSKa, Micheline. Les Appendices des Terminaux Dendrites Cérébraux et leurs différents états physiologiques. Archives des Sciences Physiques et Naturelles. Quatrième période, t. XI, May, 1901.