himself, and by my own personal observations. The third rests upon the evidence of Messrs. Schrœder van der Kolk and Vrolik, and of an eminent countryman of our own, Dr. Allen Thomson, to whom I am indebted for unpublished observations made with express reference to these very points.
1. The third lobe or posterior lobe of the cerebrum.—Many anatomists divide the cerebral hemispheres of man into only two lobes, the anterior and the posterior, separated from one another by the fissure of Sylvius; but it is more usual to speak of three lobes,[1] an anterior, a middle, and a posterior, the latter, or 'third lobe,' being the posterior, inasmuch as it consists of the hinder part of that, which those who divide the cerebral hemispheres into two lobes, call 'posterior.' It is in this sense that Cuvier, Meckel, and Tiedemann use the term third, or posterior lobe. It is generally admitted that no very strict line of demarcation is traceable between the middle and posterior lobes; anatomists being content to accept Cuvier's curt definition:—
"La partie du cerveau située au-dessus du cervelet est ce qu'on nomme le lobe postérieur du cerveau."[2]
So far as I am aware, the terms "third" or "posterior lobe," have never been applied in any other senses than those which I have indicated. Under these circumstances, it is utterly incomprehensible to me how any one competently informed, either with respect to the literature or to the facts of the case, can assert that the hind lobe "is peculiar to the genus Homo;" for not only will the inspection of any ape's brain convince one of the contrary, but the facts were originally ascertained and published by a most competent authority, and have never been doubted for nearly forty years.
Tiedemann's "Icones Cerebrorum Simiarum," published in 1821, in fact, ought to be familiar to every student of mammalian anatomy. On turning to his first Plate, one finds the first figure to be a representation of the brain of "Simia nemestrina" The explanation of the figures says: "a,
- ↑ It is not a very easy matter to determine with whom these divisions originated. Vesalius (Humani Corporis Fabrica, libri septem, MDCXLII.) speaks neither of lobes nor of special 'prominentiæ' in the cerebral hemispheres, though he describes them very accurately, explaining particularly that the under surface of these hemispheres is adapted to the 'tubera' of the cranial bones.
"Varolius (Anatomiæ sive de Resolutione Corporis Humani, libri iii., MDXCI. p. 131) says, in his letter to Hieronymus Mercurialis: 'De nervis opticis multisque aliis præter communem opinionem in humano capito observatis;'
"Sunt autem tres cerebri prominentiæ: anterior, media, et posterior . . . . . postrema cerebri prominentia replet cavitatem productam á superiori parte occipitii à posteriori ossis sincipitis et ossis petrosi.'
This looks like the origin of the division into three lobes, while Willis seems to have originated the division into two.
"Porro in homine cui cerebrum præ ceteris animalibus capax et amplum est, utrumque hæmisphærium rursus in duos lobos nempe anteriorem et posteriorem subdividitur: inter quos arteriæ carotidis ramus, utrinque instar rivi limitanei productus eos veluti in binas provincias distinguit"—Willis, Cerebri Anatome, 1664.
- ↑ Leçons d'Anatomie Comparée, 2de ed., tome iii., p. 44.
