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Show 1899.] BEAIN OF THE GORILLA. 75 the divergences from this artificially created normal. For this purpose I shall select the brain belonging to the Royal College of Surgeons. On the left side of this brain (fig. 1) there is a short prce-centralis superior roughly parallel to the fissure of Rolando. From it extends forwards the sulcus frontalis superior, divided into two by a break and apparently endiug anteriorly in a fork ; but a short furrow belonging to this system arises between the extremities of the fork and extends forward for a short distance. Again, parallel with the fissure of Rolando, but below the sulcus prcecentralis superior, is the sulcus prcecentralis inferior. Of this furrow the ramus horizontalis is very oblique and communicates with the fissure of Rolando. From the mesial extremity of the ramus horizontalis arises the very short sulcus frontalis medius. From about the middle of the prsecentralis inferior arises the sulcus frontalis inferior, which is quite as extensive a furrow as the frontalis inferior. It is roughly parallel to it. The first portion of the furrow forks exactly as does the frontalis superior, and again in the same way the distal part of the furrow arises between the fork. The sulcus fronto-orbitalis is continuous with the Sylvian fissure below, and bounds the anterior side of the (here exposed) island of Reil. In front of this is the Y-shaped sulcus fronto-marginalis; the stem is perpendicular to the long axis of the hemisphere ; finally the pre-Sylvian fissure completes the triangular boundary of the island of Reii. The right half of this brain shows the following principal differences :-The frontalis medius is much longer ; the ramus horizontalis does not communicate with the fissure of Rolando. The frontalis inferior does not communicate with the prcecentralis inferior. The prcecentralis superior nowhere differs greatly from the arrangement which obtains in the brain that has just been described. It never is continuous with the prsecentralis inferior as is the case with a Chimpanzee's brain in m y possession. The frontalis superior in other brains shows variations in the degree and manner in which it is broken up into segments. Sometimes it is a continuous fissure; this was the case with both sides of one brain and with one side of another. In the right hemisphere of a third brain the first part of this fissure became deflected to the right and joined the prsecentralis inferior (fig. 6). Prcecentralis inferior.-In three hemispheres (belongiug to different brains), in addition to the College of Surgeons' brain already referred to, the ramus horizontalis cut the Rolandic fissure. The sidcus frontalis medius is not a prominent feature of any of the brains at my disposal. The smailness of its size in the College of Surgeons' brain has been commented upon already ; it is present and also small in only one hemisphere out of the four remaining brains examined by me. In the rest I can find no vestige of it. It. might possibly be held that the furrow marked F.p.i, in fig. 6, is really a portion of the medius. But I think that |