CEREBRAL COMMISSURES IX THE VERTEBRATA. 485 



In 1892, Adolf Meyer described the commissure in Iguana and called it " commlssura 

 pallii posterior" *. 



In a series of memoirs published in 1892 and 1893, Herrick f records the presence of 

 the aberrant commissure in a series of Lacertiliau and, if I understand him aright +, 

 Ophidian brains, and adopts the same view as Edingcr. 



In a later memoir Rabl-lliickhard ("Einiger liber das Gehirn der Riesenschlange," 

 Zeitschr. f. wiss. Zoologie, Bd. Iviii.) adopted Meyer's title " commissura pallii posterior " 

 and agreed with him as to its presence in Saurians only. Thus he found it in 

 Psammosaurus, Lacerta, Iguana, Podineniu, and Chameleo, but nol in any representative 

 of the Chelonia, Crocodilia, or Ophidia. Herriek, on the contrary, somewhat vaguely 

 intimated that it is present in the Oi)hidian brain (" Topography and Histology of the 

 Brain of certain Reptiles," Journal of Comparative Neurology, vol. iii. 1893). He 

 referred to the commissurn aherram as the " hippocampal commissure," but when he 

 added that "this does not ditfer in any morphological respect from the corresponding 

 body in mammals" {op. cit. p. 89), it becomes clear that he had utterly failed to 

 a])preciate the extraordinarily peculiar features of this commissure. 



In his latest account (1896) of the commlssura aberrans, Edinger, Avho adopted the 

 term " commissura pallii posterior" committed a number of errors, which are A^ery 

 surprising when it is remembered that he had then made a series of accurate obser- 

 vations on this region of the forebrain for eight years. Thus in referring to this (with 

 the other commissures) he made the general statement " in der Lamina terminalis 

 verlaufen die Commissuren " [op. cit. 1896, p. 339), without any qualification or any 

 remark to indicate that the commissura aberrans does )iot lie in the lamina terminalis, 

 but upon the epithelial roof of the third ventricle. This statement, moreover, was not 

 due to a mere looseness of expression or lapsus calami, because in his illustration of the 

 mesial surface of the brain of Varauus (tig. 1, p. 337) he represented the doubtful 

 commissure as being attached to the upper extremity of the lamina terminalis. [This is 

 shown even more clearly in the reproduction of the same figure in his ' Vorlesungen,' 

 1896, fig. 7G, p. 120.] 



In the text of his memoir upon the forebrain of Reptiles {op. cit. 1896) he makes a 

 statement concerning the position of the commissura aberrans to the effect that '• die 

 caudale Mantelcommissur [commissura pallii posterior] liegt direkt von der Stelle, wo 

 die Hirnwand sieh zum Plexus verdiinnt, wie ich das schon in meinen ersten Mitteilungen 

 gezeichnet babe" (p. 372). This statement is in accord with the above-quoted remarks 

 concerning its relation to the lamina terminalis and is unquestionably erroneous, because 

 the commissure is placed behind, and not in front of, the situation of the mesial attach- 

 ment of the latenxl choroid plexus. This relationship is one of its most significant 

 features. 



* A. Meyer, Zeitschr. f. wiss. Zool. BA. Iv. (1892) p. Go. 



t C. L. Herrick, "Topograph}- and Histology of the Braiu of certaiu Reptiles,'' Jouni. Comp. Neurology, lby;3. 



j Jouni. Comp. Neur., Ib92, p. 179. 



