SCIENCE. 



15 



a white intercalation, and especially the outer zone (also 

 in part the inner) presents a beautiful alternation of 

 gray and white laminae. 3 



These two gray zones constitute the fundamental de- 

 marcation of the thalamus ; they may be termed zona 

 grisea medialis and zona grisea lateralis. In animals 

 above the rank of marsupials we find added a round 

 nodular mass, distinctly prominent at the ventricular i 

 floor, which lies anteriorly, while in still higher groups a 

 second nodular prominence develops posteriorly. The 

 latter is known as the posterior tubercle or pulvinarium, 

 the former as the anterior or superior tubercle. The 

 former designation seems the best to me, for although 

 what I call the undifferentiated parent mass of the thai- 

 ami is visible in sections anterior to those in which the 

 anterior tubercle is reached, yet the latter, which I pro- 

 pose to term the anterior nodule of the thalamus, is the 

 first differentiated centre reached. In man the zona \ 

 grisea medialis is faintly seen before the anterior nodule 1 

 is reached, but the anterior nodule reaches its main de- 

 velopment before the zones do, and is absent where 

 these are most prominent. In the carnivora generally, 

 the anterior nodule projects far in advance of the zones. 

 In these animals, too, a more complex arrangement of 

 this nodule is found than in man, inasmuch as the ante- 

 rior part of the internal slope of the thalamus shows sev- 

 eral elevations absent in the human thalamus. 



The 2ona grisea medialis appears pretty equally dif- 

 fused and exhibits its lamination evenly both in front and 

 in the middle of its course. The same applies to the 

 human brain lor the zona grisea lateralis. In the cat, 4 

 however, the anterior part of the external zone appears 

 as a beautiful round compact ganglionic mass, protrud- 

 ing boldly into the internal capsule, and which acquires 

 the characteristic lamination only in posterior planes. 



It is interesting to note that the ganglionic matter of 

 the thalamus is continuous with that of the ventricular ! 

 nucleus of the corpus striatum (nucleus caudatus). In- 

 directly it is connected with the extra-ventricular nucleus, I 

 through thai great common basilar gray mass, which is j 

 the rendezvous, as it were, of all the gray categories of 

 the forebrain. 5 



In an earlier publication (Architecture and Mechanism 

 of the Brain — Journal of Mental and Nervous Diseases, 

 1879), I have called attention to the fact that the ventri- I 

 cular nucleus of the corpus striatum is the representa- \ 

 tive of the primordial cerebral gray, inasmuch as the 

 nerve cells of the embryonic and lower amphibian hemi- 

 sphere are concentrated immediately subjacent to the 

 ependyma of the latter ventricle. The majority of these 

 cells i*re crowded away from the ventricular floor by the 

 white substance developed in higher animals, and only a 

 portion of the primitive gray remains subependymal. 

 This is precisely what constitutes the corpus striatum. 

 Now the corpus striatum actually lines the ventricle ; it 

 not only lies at its floor ! Any section transversely to 

 the cerebral axis and striking the forepart of the lateral 

 ventricle in the Hippopotamus, Horse, Dog or Cat, will 

 show that an attenuated part of the corpus striatum is 

 continued around over the ventricle, and* constitutes a 

 greater part of its roof. 



A similar comparative study shows that the nucleus 

 lenticularis is also a subcortical development, that is, it 

 results from the individualization of a gray mass origin- 

 ally continuous with the cortex, by means of an irruption 

 of white masses. These at first separate fasciculi (as in 



3 And yet the latest pretended description of these Ganglia, admitted, 

 notwithstanding numberless glaring errors, into a journal of the standing 

 of 'Brain (that by Dalton), has the Thalamus '* homogenous." 



* As seen in a series of transverse sections prepared by Dr. Graeme 

 Hammond. 



6 Here meet the olfactory gray, the cortex," the iasis capitis nuclei 

 cauitati, the nucleus lenticularis, the claustrum, the thalamic axial 

 gray, etc., etc. 



the dog) in higher animals coalesce to constitute the ex- 

 ternal capsule. The segmentation of the lenticular 

 nucleus into three distinct articuli so characteristic of 

 the human brain, is not found in the carnivora ; only the 

 outer articulus is demarcated, and that but imperfectly. 



In the carnivora the laminae medullares or white 

 streaks of the lenticular nucleus are conspicuously absent 

 in the anterior half of that ganglion ; in its posterior half 

 they appear and they rapidly increase in bulk as we pro- 

 ceed backwards, so that in planes where the human 

 lenticular nucleus is still quite massive, we have in the 

 dog only slight ganglionic masses intercalated between 

 the fibre tracts. The claustrum is, in the carnivora, not 

 the thin expanded lamina found in man, but a low and 

 massive accumulation, hardly separated from the cortex 

 of the Island of Reil. This fact strengthens Meynert's 

 view that the claustrum is but an individualized cortical 

 layer. 



In conclusion I would mention as an isolated fact, and 

 disconnected from the main subjects dealt with in these 

 notes, that the anteiior pyramids of the brain of the 

 large Ceylon fruit bat (Pteropus fuliginosus) undergo a 

 superficial decussation, as patent, and more so, as that 

 of the optic chiasm. The pyramidal tract after decus- 

 sating is continued as a distinct fasciculus on the lateral 

 aspect of the medulla oblongata. In the same brain the 

 fibres of the fornix can be clearly seen to terminate in 

 the thalamus without descending to the base of the 

 brain. Whether this applies to the whole of that tract, 

 I am not able to say. 



I would also note that in the brain of a large Ara 

 {Ara ararauna) obtained from the Superintendent of the 

 Central Park Zoological Gardens, Mr. W. A. Conklin, I 

 found what appeared to be a thin commissure uniting the 

 two cerebral hemispheres in their posterior half. This 

 (commissure ! if the observation was ccrrect) was not,, 

 like the Corpus callosum, a connection between the inter- 

 nal white matter of both hemispheres, but merely a union 

 of the superficial white, which in lower animals is well- 

 developed outside of the coitical gray. 



In the carnivora the Ganglion of Soemmering (the 

 Substantia nigra in the human brain) is continuous with 

 the innermost part of the lenticular nucleus. This fact 

 strengthens Meynert's proposition, that the Ganglion of 

 Soemmering, like the caudate and lenticular nuclei, should 

 be considered as parts of one system, whose ganglia are 

 connected with the fibres of the pes pedunculi. 



In the elephant, whose brain, both in its mass, the pre- 

 ponderance of the hemispheres, and the concealment from 

 view of the so-called "trapezium," takes a high rank as 

 regards the grade of development, I had the opportu- 

 nity to make and examine transverse microscopic sec- 

 tions from the Pons Varolii. The remarkable discovery 

 was made that the descending (longitudinal) fibres of 

 the Pons are wanting. Nothing but transverse fasciculi 

 are seen in the field. Since the former fibres constitute 

 part of the pyramidal tract, it follows that the tract of 

 the voluntary impulses, the " will-tract," must take 

 another course in the elephant, one which may be con- 

 sidered aberrant ; for in all other placental animals so 

 far examined by myself, the pyramidal tract runs 

 through the Pons Varolii, as in man. 



On Waldivine. — Waldivine, C36H24O20, is a neutral 

 principle, without rotatory power, very sparingly soluble 

 in cold water, freely soluble in chloroform, insoluble in 

 ether, and remarkable for the ease with which it is decom- 

 posed by alkalies. 



Certain Optical and Visual Phenomena — If the 

 flame of a lamp is viewed through a nairow slit, the lustre 

 of the.flame and the effects of diffraction vary much accord- 

 ing as the slit is vertical or horizontal, the light being much 

 more considerable in the latter case. — M. Treve. 



