50 DR. G. ELLIOT SMITH ON THE 



same time we will see how tlie latter explains mucli that is apparently meaningless and 

 purposeless in the ontogenetic process. 



From the foregoing remarks concerning the scope of this investigation, it must he 

 evident that we are mainly concerned with the hippocampal region of the two types of 

 cerehrum. In other AA^ords, we are going to study and compare the dorsal commissure 

 of the Marsupial, which is " hippocampal," with its topographical representative 

 in the bat, which is mainly " hippocampal." It is therefore necessary to have a 

 clear and definite idea of disposition of the hippocampal region of the Metatheriau 

 cerehrum ; and we may first of all consider the hippocampus of Pcrmncles nasiita, which 

 exhibits very clearly the distmctive features of the Marsupial brain (mainly by means 

 of sections stained by the Weigert method). 



I have not yet been fortunate enough to get specimens of the brain of Nyctophilus in 

 a condition suitable for the application of the Weigert stain. But the resemblance 

 to the Marsupial type is so great that with the aid of the lithiiun carmine stain 

 quite sufficient detail can be made out to reveal the distinctive features of the region 

 with which we are concerned. I hope soon to be able to supplement these notes by a fuller 

 paper on the brain of Nyctophilus, studied by more specialized neui'ological methods*. 



My friends Mr. James P. Hill and Mr. J. Macpherson, of the University of Sydney, 

 very kindly placed at my disposal four brains of NijctopMlus which were in a good state 

 of preservation, though hardened only in alcohol. My friend Dr. R. Broom, who was 

 at Taralga working at the organ of Jacobson in Iliniopterus, kindly gave me the brain 

 from one of his specimens. Mr. Robert Grant, the able assistant in the Physiological 

 Laboratory at Sydney, stained and cut series of coronal, sagittal, and oblique sections 

 from these specimens. To these gentlemen I acknowledge my deep gratitude and great 

 indebtedness. 



This Avork was done mainly in the Anatomical Department of the University of 

 Sydney, and has been completed — so far as such an unfinished work can be said to be 

 — in Cambridge. 



The Hiirpocampal JRegion in the Marsupial. 



The mesial wall of the descending limb of the lateral A'entricle of the cerebrum of the 

 Marsupial presents a marked prominence, which extends in the long axis of the ventricle. 

 This is the hippocanqyus — the homologue of the hippocampus major of the Primate brain. 

 In its histological structure and in the disposition of its constituent parts this region of 

 the Metatherian cerebral hemisphere agrees exactly with the corresponding part of the 

 Eutherian, so that in seeking for distinctive features of the two types of brain it 

 may be neglected. We will therefore begin the study of the brains under consideration 

 at a point just in front of the place where the lateral ventricle begins to curve doAvuAvard 

 to form its descending cornu. 



The first figure (PI. 15. fig. 1) represents a coronal section through the forebraiu of 



* Since this Tvas -n'ritteii I have coiifinned, by menus of i>re]iaratioiis stained by Weigert's method, all the 

 observations concerning JS'i/ctojihiltis which are here recorded. 



