512 'Journal of Comparative Neurology and Psychology. 



in this bj tiie Basle nomenclature commission and the tables of 

 neurological terms adopted by the commission contradict His's 

 explanatory notes in that the tables place the pars optica hypothalami 

 in the diencephalon while His states that it belongs to the telen- 

 cephalon. (See His, 1895, pp. 161, 162.) This is perhaps because 

 anatomists generally have felt the incongruity of assigning the tuber 

 cinereum, infundibulum and hypophysis to the telencephalon. This 

 objection fails when only the chiasma and the fiber decussations 

 adjacent to it are included in the telencephalon. 



The usage adopted by the BN'A goes to the other extreme and 

 involves at least as bad consequences. The BNA includes the lamina 

 terminalis in the pars optica hypothalami, and implies that the 

 lamina terminalis is the front wall of the diencephalon. The discus- 

 sion of this usage, which is widely followed by anatomists, will come 

 best in the next section, but here it may be pointed out that it implies 

 the inclusion in the diencephalon of various structures which cer- 

 tainly can not be so interpreted. 



a. The lamina terminalis contains the anterior commissure, and 

 according to the researches of G. Elliot Smith the corpus callosum 

 and hippocampal commissure develop in it also. These commissures 

 would then all fall in the anterior wall of the diencephalon. This is 

 obviously impractical and confusing and would lead to endless diffi- 

 culties in fixing an arbitrary boundary. 



6. The gray matter in the wall of the preoptic recess constitutes 

 generally in vertebrates an important secondary olfactory center 

 which, unless there are strong reasons for assigning it to the dien- 

 cephalon, should be placed with the other secondary olfactory centers 

 in the telencephalon. All the facts of development and general mor- 

 phology, however, favor the retention of this center in the te]en- 

 cephalon. 



c. In many fish-like vertebrates the larger part of the telencephalon 

 (corpus striatum and olfactory lobe) lies lateral to the lamina 

 terminalis and forms the wall of the median ventricle. These struc- 

 tures in fishes would be included in the diencephalon and there would 

 be endless confusion as to the boundary line in various classes. ISTo 

 such confusion and no practical difficulties in the description of the 



