8o Journal of Comparative Neurology. 



the writer in fishes and the opossum and by Professor C. Jud- 

 son Herrick in rodents and we have agreed in tracing the lateral 

 radix along the fissura radicis to the pyriform lobe where' the 

 tract either splits or is met by fibres from the supra-commissure 

 tract. The fibres remaining in the cerebrum spread out over 

 the pyriform and can be traced more or less directly to the hip- 

 pocampus. In fishes where the hippocampus is not differenti- 

 ated from the "occipito-basal lobe" (homologue of the pyri- 

 form) the fibres pass, in a continuous sweep, from the olfactory 

 tuber to the point where the hippocampus would appear. Dr. 

 Edinger agrees with our suggestion that the latter body may be 

 looked upon as an outgrowth from the occipito-basal lobe. 



In reptiles we have found a similar arrangement. Dr. Ed- 

 inger's recent paper follows the radix lateralis in the turtle 

 through the occipito-basal lobe ( "nucleus spheericus") to the 

 cortex of the Ammonshorn. 



Dr. Meyer, in his discussion of the olfactory radices', says 

 that the great majority of the fibres of the olfactory tract assem- 

 ble laterad of the ventricle and thence pass to the nucleus 

 sphaericus, where, apparently, the fibres, after losing their 

 sheaths, break up into fine terminal brushes and are distributed 

 to the inner portion which is poor in cells but is surrounded by 

 a dense layer of cells, like a cap. According to our observation, 

 however, this which has been regarded as a core of the organ is 

 really but an invaginated portion of the caudo-ventral surface. 

 It is so folded that the olfactory radix is included within the 

 groove-like entrance and conducted into the central (morpho- 

 logically ectal) space, where they spread out just as in other 

 reptiles, If Dr. Edinger is correct and the nucleus sphaericus 

 belongs specifically to the hippocampus then the fact that the 

 radix lateralis fibres cannot be as distinctly traced to the free 

 cortex as in other reptiles need produce no surprise. However, 

 in suitable sections fibres can be traced from the nucleus sphaer- 

 icus to the caudal cortex or hippocampus proper. 



Dr. Meyer adds: " It is indubitable that other olfactory 



^Zeitsch. f. wiss. ZooL, LV, i. 



