THE BEAIX IN THE EDENTATA. 333 



It seems to me that the su;^gestive mass of evidence in favour of the view that the 

 " retro-limbic tissure " of Quadrupeds is tlie homologue of the calcarine sulcus of Primates 

 cannot be lightly gainsaid.] 



The great bulk of the litei'ature relating to the brain in the Edentata is mainly con- 

 cerned with the cranial aspect of the pallium. But altliough this is the case, the 

 information to be culled from a study of this mass of descriptive matter is of a very 

 imperfect and in many ways an unsatisfactory nature, for our methods and ultimate 

 aims in investigating the anatomy of the brain are now vastly different from those 

 which inspired the authors of the records which we find so disappointing in their 

 insufficiency. It would therefore be hardly justifiable to enter into a serious discussion 

 of many aspects of tlie study of the surface of the brain which take a foremost place 

 in the memoirs to which reference will be made. 



It will conduce to clearness in the description of the surface of the pallium in this order 

 if we begin Avith the. consideration of Myrmecophaga, in which the fissures very clearly 

 conform to a Avell-recognized type. 



In the memoir of Gervais * we iind excellent representations of the conformation of 

 the pallium in a specimen of Myrmecophacja, as well as a figure of a cranial cast of 

 another specimen. In the more recent memoir of Forbes f Ave find some very useful 

 semi-diagrammatic figures of the brain in two specimens of Ilynneeojjhaga. My 

 observations were made upon two specimens in the galleries of the Iloval Colleo^e of 

 Surgeons ; but, as one of these brains AA'as still clothed Avith its membranes, practically only 

 one Avas available for examination. A partially-dissected specimen of the brain of 

 Myrmecophaga in the stores of the College enabled me to investigate many pioints in its 

 internal anatomy. Figure 7 represents the left lateral aspect of one of the brains of 

 Jlyrmecophaga in the College of Surgeons, and may serve as a type upon Avhich to base 

 our description. 



The A^entral boundary of the pallium is formed by the rhinal fissure, Avhich consists of 

 an approximately parallel anterior segment passing by a regular arcuate course 

 directly into the posterior rhinal segment. The latter forms an angle of about 120^ with 

 the former, and hence the posterior part of the pallium descends to the base of the brain 

 as a large dependent process behind the pyriform lobe. Above the point of junction of 

 the anterior and posterior rhiual fissures Ave find a triangular depressed area of pallium, 

 Avhicli we may distinguish as the fossa Sylvii. Its posterior border is formed by a 

 vertical lip which begins below at about the mid-point of the oblique posterior rhinal fissure. 

 As it ascends this lip diverges from the lip formed by the pyriform lobe at the posterior 

 rhiual fissure, and AA-hen it has reached a point about 7 mm. from the dorsal surface of 

 the hemisphere (vicAved in profile) it curves backward for a short distance and terminates 

 suddenly. Thus Ave find the fossa Sylcii limited below and behind by two prominent 

 arcuate lips, the convexities of Avhich face one another. These lips meet below, but above 

 and in front they are widely separated. In this broad interval the depressed area of 



* P. Gervais, op. cit. pi. i. figs. 3, 3a, and '3h, and pi. ii. fig. 3. 

 t W. A. Forbes, op. cit., Proc. Zool. Soc. London, 1882. 

 SECOND SERIES. — ZOOLOGY, VOL. VII. 46 



