104 THE VOYAGE OF H.M.S. CHALLENGER. 



brains were 22 mm. long by 11 mm. broad. Each possessed a peduncle which in two 

 brains was 3 mm. broad but 6 mm. in the third. The peduncle was placed on the 

 olfactory sulcus, but was not concealed within it. This peduncle terminated behind in 

 a distinct tuber olfactorium (to), 21 mm. long by 6 mm. broad, which passed backwards 

 and outwards into the Sylvian fossa and joined the anterior end of the lobus hippocampi ; 

 from the olfactory tuber a band, which formed an inner root, passed inwards to the mesial 

 longitudinal fissure and the gyrus rectus. The optic tracts and nerves were from 2 to 

 3 mm. broad ; the nerves and commissural end of each tract were rounded cords, the 

 outer part of the tract formed a flattened band winding round the outer side of the crus 

 cerebri, and was traced to the posterior end of the optic thalamus ; the optic commissure 

 was smaller than in the human brain. Behind the commissure was a broad tuber cinereum, 

 from which the dilated infundibulum proceeded to the pituitary body. This body, the 

 hypophysis cerebri, was indented as if divided into two lateral and two median lobes, of 

 which the postero-median was much smaller than the antero-median and the lateral (PI. X. 

 fig 6). Corpora albicantia were not recognised. The crura cerebri were massive, diverged 

 from each other, and had between them the tuber cinereum and grey matter of the locus 

 perforatus posticus. The ventral surface of each crus was flattened and marked with 

 fasciculi, some of which ran in the long axis of the crus, whilst others formed on the 

 surface a raised bundle, which curved from within outwards. The third nerve was a little 

 larger than in man, and arose from the inner side of the crus. The fourth nerve was 

 similar in size and position to the human nerve. 



Convolutions and Sulci. — The Sylvian fissure (s) commenced in the Sylvian fossa at 

 the locus perforatus anticus ; it passed at first almost transversely outwards, and then 

 mounted upwards and somewhat backwards in the notch on the side of the hemisphere 

 already referred to, and ended in two short branches of bifurcation. The Crucial fissure (c) 

 was not visible on the vertex, but was situated at the anterior end of the hemisphere 

 immediately above the olfactory bulb ; it was short and passed outwards and slightly 

 downwards. The sigmoid gyrus which bounded it was comparatively slender, and in 

 brain c, though not in a, was concealed at its outer end in the coronal fissure owing 

 to the overlapping of that fissure by the broad anterior end of the mediolateral 

 convolution. It is doubtful if either a prrecruciate fissure or ursine lozenge can be 

 said to exist. 



The sujiraorbital area of the hemisphere was bounded in front and above 

 by the crucial fissure, and behind and below by the Sylvian fossa and com- 

 mencement of the Sylvian fissure and the locus perforatus anticus. In this area 

 the olfactory fissure was situated parallel to the longitudinal fissure and concealed 

 by the olfactory peduncle; a well-marked rhinal fissure (rh) extended backwards and 

 outwards from the olfactory fissure, and, bounding externally "the tuber olfactorium, 

 passed deeply into the Sylvian fissure. An intraorbital fissure (io), which, whflst repre- 



