88 Journal of Comparative Neurology. 



are motor. This belief, being founded not simply upon an anal- 

 ogy in appearance but upon the fact that the ventral peduncu- 

 lar bundle distributes its fibres to these regions ; we cannot 

 agree with those writers who claim the whole cortex for sensory 

 apparatus, still less with those who appropriate it to the olfactory 

 sense alone. 



There is a rudimentary rhinalis fissure separating a ventral 

 region devoid of cortex from one which although flanked by the 

 central lobe still has a cortical differentiation. We have noth- 

 ing to add to the description of the intra-ventricular lobe, or 

 that part of the mesal walls which lies ventrad of the fissure. 

 This is not cortical in structure and is wonderfully similar to the 

 corresponding part in the opossum (we are not prepared to use 

 the term septum pellucidum for this structure.) 



As we pass caudad the peduncular fibres accumulate on the 

 mesi-basal aspects and the occipito-basal lobes appear along the 

 latero-basal aspects {f?[^s. -/-J. Fibres from the fronto-median 

 lobe gather near the mesal fissure and accumulate dorsad of the 

 intra-ventricular lobe, which now is forming a transition into 

 what must be called corpus fornicis. The callosal fibres (in ac- 

 cordance with the usage of Osborn) pass from the fronto-median 

 lobe of one side to the other, not without decussations but in 

 just the same sense as in higher vertebrates. Before one can 

 unhesitatingly commit himself to a term as much mooted as this 

 one it is desirable to secure a unambiguous definition of it. This 

 we evidently cannot soon expect. We propose for the present 

 to consider as a callosum any bundle of nerve fibres passing 

 from the dorsal cortex of one side to the dorsal cortex of the 

 opposite side cephalad of the fornix. It shall not be obligatory 

 to determine whether the parts connected are homologous or 

 otherwise for the latest admissions of Meynert left us in doubt 

 whether such fibres are characteristic of the human callosum. 



The above definition excludes the commissure described 

 by the the writer in fishes though recent studies have added ev- 

 idence in favor of the hypothesis that homologues of cortical 

 niduli may remain in the axial lobes. What was intended by 

 the employment of the term callosum in that connection was to 



