48 



Dr. C. I. Forsyth Major. 



of the smaller animal exceeded that of Megaladapis. So far as can 

 be judged from the cast (fig. 4), the hemispheres were much less 

 convoluted than in the large existing recent Lemurids, their fore- 

 and hind-parts being apparently almost smooth in the fossil form. 



The reduced proportions of, or, more properly speaking, the 

 absence of, the occipital lobe, is testified by the cerebellum remaining 

 uncovered. 



But the most remarkable character is exhibited by the anterior 

 beak-like continuation of the hemispheres (fig. 5, b), which presents 

 in section a triangular form with a broad, flattened base and a 

 trenchant superior margin. The corresponding part of the skull has 

 been elsewhere described,* when it was shown that the correspond- 

 ing constriction of the brain cavity is due to the enormously 

 developed frontal sinuses protruding into the anterior portion of the 

 cerebral and olfactory fossa?. 



The optic nerves will help us by indicating the orientation in this 

 curiously shaped brain (fig. 3 and fig. 6). From a comparison of 

 the inferior part of the brain of Megaladapis with that of an Indris 

 (fig. 7), it will be seen that in the former the frontal lobes are 

 absent, and the part of the hemispheres situated in front of the 

 optic nerves is represented by scarcely anything but the posterior 

 part of the before-mentioned beak (fig. 6, b ), which continues anteriorly 

 to form the olfactory tract which is equally reduced, Even in croco- 

 diles (fig. 8), the fore part of the hemispheres, anterior to the optic 

 nerves, appears less reduced than in this Mammal. 



Little information can be obtained as to the anterior portion of the 

 tractus and the bulbi, as it was not possible to mould this portion 

 of the narrow channel running between the internal walls of the 

 frontal sinuses ; nor could this unique skull be bisected. As far as 

 can be made out, the canal in question widens in proximity to the 

 cribriform plate, so as to form the chambers for the lodgment of the 

 olfactory bulbs.f 



* " On Megaladapis madagascariensis , an extinct gigantic Leniuroid from Mada- 

 gascar, &c," 'Phil. Trans.,' B, vol. 185, 1894, pp. 25, 26. 



f A somewhat similar conformation obtains in the Whales, to which my attention 

 has been drawn by Sir William Flower, who described it in Balcena mysticetus, 

 where " the two somewhat dilated chambers for the olfactory bulbs are divided from 

 the cerebral cavity by a canal which runs for a distance of 8| inches and is 1% inches 

 wide and from i to 1 inch high." { On the Greenland Eight-Whale {Balcena 

 mysticetus) ,' by D. F. Eschricht and I. Bernhardt; Appendix by the editor, 

 William Henry Flower, London, Ray Society, 1866 ; W. H. Flower, ' An Introduc- 

 tion to the Osteology of the Mammalia,' 3rd ed., London, 1885, p. 220. See also 

 Ant. Desmoulins, ' Diet. Class. d'Hist. Nat.,' vol. 6, 1824, p. 372, s. v. " Event " 

 {Balcena australis) ; F. Cuvier and Laurillard, in ' Cuvier, Lecons d'Anat. Coinp.,* 

 seconde edit., vol. 2, 1837, p. 305 (Balcenoptera) ; Otto Kostlin, ' Der Bau des 

 knochernen Kopfes in den vier Klassen der Wirbelthiere,' Stuttgart, 1844, pp. 16, 

 17, 18, 89 (Balcena australis — Balanoptew borealis). 



