loS Journal ok Compakativk Neurology. 



It atVords me pleasure to state that my observations upon 

 this commissure substantiate and extend those of Meckel 

 and Professor Osborn. My sections show a corpus callosum, 

 not only in the brains of the lower type of birds, but also in 

 the encephala of the highly-specialized Passerine group. 

 Therefore, I think we may safely emphasize the statement 

 that all birds have a corpus callosum.(') 



Errata. — Before proceeding, I would like to correct a 

 couple of misprints that crept, unobserved, into the first 

 paper of this series. The first occurs on page 57, seventh to 

 ninth lines. Those lines should read: "The waders and 

 fowls and their afRnes are placed in group ' B.' The re- 

 mainder of the carinate birds fall in group ' A.' " The 

 second error occurs on page 91. The last statement in the 

 explanation of Figure 3 of Plate VII should read: " S. C, 

 posterior commissure." 



Technique. — Additional remarks upon the methods em- 

 ployed may seem superfluous. It must be remembered, 

 however, that different tissues require difi'erent treatment. 

 In the prosencephalon, where tracts are few and quite dis- 

 tinct, a stain that diflferentiates cells well, even though it 

 does not dye the fibres, is all-sufficient. In the diencephalon 

 and mesencephalon, however, where fibre tracts are numer- 

 ous and somewhat intermingled, it becomes imperative to 

 use a stain that differentiates fibres. While looking gbout for 

 a good fibre stain, Kolliker's article, "Zur feineren Anatomic 

 des central Nervensystem,"(') was referred to. The plates 

 illustrating that article are excellent. In them the finest 

 nerve fibres are depicted. The sections from which these 

 remarkable plates were drawn had been prepared by 

 Golgi's shorter method, (■) and I determined to test the 

 application of the method to avian brains. The brain of a 

 pigeon {Coluuiba livia) was selected for the experiment. 



1 Journal of Comtarative Neurolo(.v, Vol. I, p. 76. 



2 Zeit. f. wiss. Zool., Bd. LI, taf. i-vi. 



3 Op. cit., Bd. LI, p. 9. 



