228 H. F. Osborn 



with the corpus callosum neither in position, nor does this view accord 

 with the facts of the development of the corpus callosum. He in- 

 clined rather to compare it with the commissural portion of the fornix, 

 although this was also uncertain. The same author (1881 pag. 282), 

 described the lower bundle in Psammosaurus as consisting of 

 fibres connecting the brain stem of the opposite sides, and besides 

 this, fibres passing from the stem region of one side to the medial 

 mantle of the other forming the chiasma partis olfactoriae, 

 (pars olfactoria). The hemispheres are further connected by a com- 

 missure in the roof of the S'"^ ventricle behind the foramina of Monro, 

 which passes laterally downwards into that part of the wall of the 

 hemispheres which may be compared to the cornu ammonis. This 

 he considers a rudiment of the fornix, or the commissure of the cornu 

 ammonis (Foeel). 



Later (1 883 pag. 304) this author writes as follows: »Diebeiden 

 Abschnitte der Commissura anterior finden sich überall, bei den Rep- 

 tilien, bei den Sauriern namentlich prächtig entwickelt, schwächer 

 beim Alligator .... Als letztere (Pars olfactoria) kann tiberall nur 

 dasjenige Bündel gelten, welches nach vorn zu in den Mantel des 

 Stirnhirns einstrahlt und hier wahrscheinlich weiter zieht; während 

 dieser Mantel zur Wand des hohlen Riechlappens wird.« This was 

 partly written upon the authority of Mihalkovics (1875) who spoke 

 against Stieda's view of the upper bundle in the Turtle upon the 

 sole ground of Stieda's very doubtful observation of the course of 

 the similar upper bundle in the Amphibia. 



Rabl-ROckhaed's observations, which are only preliminary to a 

 fuller treatise, are of especial value as showing the invariable divi- 

 sion of the cerebral commissures throughout the Reptiles, as I have 

 found them throughout the Amphibia, into well distinguished upper 

 and lower bundles. It will be observed however that he offers no 

 positive observation upon the distribution of the upper bundle. 



Birds. 



I owe to Stieda's bibliography a reference to the very interesting 

 paper upon the brain of the Duck, written by Meckel in 1810 (181(3 

 pag. 73). The accuracy of observation which distinguished this author 

 enabled him to discern above the anterior commissure a very small 

 bundle, about Yo as large: )>Biegt man die Hemisphären von vorn 

 nach hinten so weit aus einander, dass man im Grunde der Spalte 



