198 
ME. W. H. ELOWEE ON THE POSTEEIOE LOBES 
purpose to give a description of the external characters of this brain, but only an account 
of such parts of the internal structure as have special reference to the subject of this 
paper. A horizontal section of both hemispheres has been made at the level of the 
corpus callosum, and the lateral ventricles are laid open. Fig. 15 (Plate III.) represents 
this dissection. A broad and very distinct posterior cornu extends backwards almost to 
the extremity of the hemisphere. Its floor and inner wall are raised into a prominence, 
having distinctly the characters of the hippocampus minor as found in Man and the 
higher Qnadrumana, and corresponding with the deeply marked calcarine sulcus on the 
inner face of the lobe. The form of the eminence is somewhat triangular, the apex 
being directed backwards ; but its surface is convex, both from above downwards and in 
the antero-posterior direction, so that the axis of the cavity into which it projects, 
though directed generally backwards, has first an outward inclination, and finally turns 
somewhat inwards. The anterior or broad end of the eminence is concave, being 
adapted to the curved posterior margin of the hippocampus major, from which it is 
separated by a deep groove. The length of the hippocampus minor is one-fourth of an 
inch ; its breadth at the base almost as much. The part of the outer wall of the ven- 
tricle which projects into the angle between the hippocampi may be compared with the 
“ eminentia collateralis ” of the human brain *. 
On comparing the posterior lobe in Galago with the same part in the true Apes, it is 
seen that there is, as in Lemur, a very marked reduction in length. This abbreviation is 
the more remarkable as there is no approach to it in the lowest of the Platyrrhine 
Monkeys. In the possession of a well-defined Sylvian fissure, a median lobe, and a 
calcarine sulcus, and in the general characters of the convolutions of the hemispheres, 
the brain of the Lemuridse follows precisely the same type as that upon which the brain 
of Man and the other Quadrumana is formed, and differs essentially from that of the 
Carnivora and all other orders of Mammalia. But while the gradations of the brains 
of this type are tolerably regular and unbroken between the largest and the smallest of 
the series (i. e. Homo and Ha^ale), the Lemurs do not continue in precisely the same 
line of degradation, but rather should be placed as a small subseries parallel to the lower 
part of the large series, and distinguished from it by the shortness of the posterior lobes, 
the large size of the olfactory bulbs, and the inferior condition of the cerebellum. 
With regard to the general characters of the posterior lobes throughout the series, 
although the examination of all the forms is not yet complete, the facts which have 
already been brought together are sufiicient to justify the following conclusions : — 
* A fartlier examination of this specimen, and of the brains of some allied genera, leads me to doubt 
■whether the above-described ‘ cavity ’ in the posterior lobe existed before dissection, the length of time that 
it had been in spirit having greatly facilitated this process. If it did not, it will justify the statement of 
the absence of the hippocampus minor by anatomists who have looked at this structure only in its relation 
to the posterior cornu, but at the same time wid afford a further illustration of what I have endeavoured to 
show throughout this paper, viz. that the part of the brain to which this term has been applied can exist inde- 
pendently of the ventricular ca-vity. 
