MOEPHOLOGT OF THE BRAIX IX THE MAMMALIA. 3So 



(leA-elopmontal history, wliicli thorouglily e.stablishes the homology. In some of the 

 larger Ungulata, for example Cameliis, tliere is a small posterior cornu into which 

 the " spleuial " eminence projects just as the calcar hulges into the Primate ventricle. 

 In the Cetacea the splenial sulcus is obviously identical with that of the Carnivora and 

 Ungulata, and its resemblance to the calcarine sulcus of the Primates is enhanced in 

 some genera, e. g. HijperoodoH, by its relation to a distinct posterior cornu of the 

 ventricle, wliicli has been described by Ziehen *. 



During my investigations on tlie brain in the Edentata, the results of which were 

 presented to this Society almost four years ago, I was very much astonished to lind 

 a well-defined swelling on the mesial wall of the lateral ventricle of Orycteropus which 

 simulated the calcar avis. ]\Iy astonishment was due to the fact that at that time I was 

 not acquainted with any of the above-mentioned Avritiugs and knew only of the teaching 

 of such anatomists as Plovver, Turner, and Cunningham, who have so formally and 

 categorically denied the possibility of bomologizing the calcarine sulcus of the I'rimates 

 with the spleuial furrow in other mammals. Nevertheless the mass of evidence in 

 lavour of the identity of these two furrows, which a study of the Edentata and other 

 mammals yielded, seemed to me to be so overwhelming, that I adopted this view even 

 though it is in direct contradiction to the \iews of those anatomists, from Avhom I have 

 acquired much of my knowledge of the mammalian brain f. 



Among the heterogeneous collection of Edentata, there are found all stages in the 

 form of the calcarine sulcus intermediate between the Carnivore condition on the one 

 hand, and the simpler form fouiul in the Chiroptera, Marsupialia, and Insectivora {i. e. if 

 GaleopitJiec/ts can be called an Insectivore). In no true Insectivores is there a calcarine, 

 or "splenial" (as most anatomists would call it) sulcus. But this is not necessarily 

 of any great significance, because in tlie smaller Chiroptera and (Polyprotodont) 

 Marsupials there is no such sulcus, although the larger members of these Orders 

 {Fteropus, Cyiioityderis, Thyhiciuns, and practically all the Diprotodontia) present 

 a typical one. 



The most peculiar fact, so far as the distribution of this furrow is concerned, is 

 its absence in most of tlie Ilodentia. In only one or two of the largest members of the 

 Orders, such as JlydrudiaTiis, is any such furrow developed ; and even in these few 

 cases it is small and insignificant. In the Mouotremata the calcarine sulcus cannot 

 be recognized ; moreover, it is highly probable that none of the mesial sulci in the 

 hemisphere of Echidna represents the calcarine sulcus of the Metatheria and Eutheria. 



The most primitive form of the calcarine sulcus is seen to best advantage in such 

 brains as those of ThyJaciniis, Trichosurus, F/nisco/arcfus, JIacropns, Cynoiiycteris, 

 Fteropus, and most of the Edentata. Of these I select for representation tlie hemi- 

 sphere of Pteropus poUocepjlialus, not that it diff'ers in any respect from any of the other 

 forms enumerated, but because the presence of the calcarine sulcus in this genus has 



* W. Kiikeuflial and Th. Zielcf)i, " Ueber das Centraliierveusvstem der C'o'taeeeu. iiebst Untersuchungen iibc-r 

 die yergleioheude Anatoruie der I'laceiitalicr,"' Denkscbrifteii der mediciii.-naturwisseusch. GesellscUaft zu Jeca, 

 1893, pp. 89, 117, inter alia. 



t Trans. Linn. Sue. ser. 2, ZooL vii. 1S99. pp. 32^ ;JL!3. 

 SECOND SERIES.- ZOOLOGV, VOL. VIXI, 56 



