Thus, every original authority testifies that the presence of a third lobe in the cerebral hemisphere is not "peculiar to the genus Homo," but that the same structure is discoverable in all the true Simiæ among the Quadrumana, and is even observable in some lower Mammalia; and any one who chooses to take the trouble to dissect a monkey's brain, or even to examine a vertically bisected skull of any of the true Simiæ, may convince himself, on the still better authority of nature, not only that the third lobe exists, but that it extends to the posterior edge of, if not behind the cerebellum.
2. The posterior cornu.—In the "Icones," already referred to, Tiedemann not only described but figured the posterior cornu of the lateral ventricle in the Simiæ (Tab. 2°, Fig. 3a), as "e. scrobiculus parvus loco cornu posterioris;" and when giving an account of the brain of the seal (Tab. 3a), he says: "e. cornu descendens s. medium. Præterea cornu posterioris vestigium occurrit."
Tiedemann's statements are confirmed by every authoritative writer since his time. According to Cuvier[1] (Leçons, T. iii., p. 103), "the anterior or lateral ventricles possess a digital cavity [posterior cornu] only in man and the apes. This part exists in no other mammifer. Its presence depends on that of the posterior lobes. In the seals and dolphins alone, in which the posterior part of the hemisphere is considerable, the lateral ventricle, at the point where it descends into the temporal tuberosity, bends a little backwards, thus exhibiting a sort of vestige of the digital cavity of the human brain."
Vrolik (Art. Quadrumana, Todd's Cyclopædia), though he carefully enumerates the differences observable between the brains of the Quadrumana and that of man, does not think of asserting the absence of the posterior cornu. And lastly, Schrœder van der Kolk and Vrolik (op. cit., p. 271), though they particularly note that "the lateral ventricle is distinguished from that of man by the very defective proportions of the posterior cornu, wherein only a stripe is visible as an indication of the hippocampus minor;" yet the figure 4 in their second Plate shows that this posterior cornu is a perfectly distinct and unmistakeable structure, quite as large as it often is in man. It is the more remarkable that Professor Owen should have overlooked the explicit statement and figure of these authors, as it is quite obvious, on comparison of the figures, that his wood-cut of the brain of a Chimpanzee (l. c, p. 19), is a reduced copy of the second figure of Messrs. Schrœder van der Kolk and Vrolik' s first Plate.
As M. Gratiolet (l. c, p. 18), however, is careful to remark, "unfortunately the brain which they have taken as a model was greatly altered (profondément affraissé), whence the general form of the brain is given in these plates in a manner which is altogether incorrect." Indeed, it is perfectly obvious, from a comparison of a section of the skull of the Chimpanzee with these figures, that such is the case; and it is greatly to
- ↑ Leuret, Longet, and Stannius, agree with or, perhaps, only repeat Cuvier.
