389 



commissure invading the alveus of the dorsal hippo- 

 campi) does not exist in the Marsupialia, it is represented by a homo- 

 logous bundle, which passes from one hemisphere to the other via the 

 external capsule and the ventral commissure 8 ). 



Even if Zuckerkandl had demonstrated his contention it would 

 not have appreciably affected the importance of the fact that homo- 

 logous neopallial areas in, say, Perameles and Erinaceus emit 

 commissural tracts which, in the former (Marsupialia), cross the mesial 

 plane in the commissura ventralis and in the latter (Insectivora) in 

 the commissura dorsalis. 



The "Commissura superior". 



An emphatic protest must be made against Zuckerkandl's 

 adoption of Ziehen's misapplication of the term "commissura superior". 

 When the latter first misused this term I called attention 9 ) to the 

 fact that it had been applied to the "commissura habenulae" more 

 than nine years previously by Osborn and had been widely adopted 

 in this sense by innumerable writers in all parts of the world 10 ). 



Such confusion between the names of the hippocampal and the 

 habenular commissures is especially to be avoided, because it has on 

 several occasions happened that the commissures themselves have 

 been mistaken the one for the other in the Reptilian brain. It was 

 the knowledge of this fact, which led me to consistently avoid the 

 use of the term "superior" and adopt the name "dorsalis" in reference 

 to the hippocampal commissure. If Ziehen and his followers con- 

 tinue to persist in the use of the term "superior" in spite of these 

 considerations an intolerable state of confusion will be introduced when 

 the commissures in this region of the brain are compared, say, in the 

 Amphibia, Reptilia and Mammalia. 



Thus in the Amphibia commissural fibres from the caudal part 

 of the cerebral hemispheres cross the roof of the third ventricle along 

 with (but in front of) the habenular commissure and two commissures 

 are usually included in the one title "commissura superior" (Osborn) 

 by most writers. In the Lacertilia and in Sphenodon a tract of 



8) Opera cit. supra, more especially "The Origin of the Corpus callo- 

 sum"; also "On a Peculiarity of the Cerebral Commissures in Certain 

 Marsupialia", Zool. Anz., Bd. 25, No. 678, 7. Aug., 1902. 



9) Further Observations on the Brain in the Monotremata. Journ. 

 of Anat. and Physiol., Vol. 33, 1899, p. 334. • 



10) See, for example, the references to this commissure in Pkenant's 

 "Elements d'Embryologie", T. 2, 1896, p. 627 and elsewhere. 



