234 H. F. Osborn 



forwards and scatter beneath the peduncles. The middle bundle of 

 this group cm" (figs. 1, 3 and 5), is sharply defined, and form sa com- 

 pact bundle of large fibres, extending directly outwards and slightly 

 forwards. After subdividing, it enters a network of fine fibres which 

 is traversed by the cerebral peduncles. The upper bundle is much 

 the largest. Immediately in front of it is a smaller bundle which 

 for reasons given below I have placed with the olfactory commissural 

 group. The main upper bundle cm'" (figs. 1, 4, 5), is composed of 

 fine fibres among which are a few scattered nuclei. The bundle has 

 a faint division into two parts; the upper part spreads upwards 

 directly into the hemisjjheres ; the lower part extends downwards 

 and, in the same manner as the middle bundle cm" ^ enters a mesh- 

 work of fibres, intercalating between the cerebral peduncles, and 

 spreading beyond into the hemispheres. 



II. Commissural fibres and tracts of the olfactory 

 lobes. I have not succeeded in determining with the completeness 

 shown in Bellonci's paper, the relations of the olfactory lobes with 

 each other and with the hemispheres. I have observed however a 

 tract passing directly from the central olfactory region and spreading 

 into the hemispheres. Secondly, a tract extending from the cerebral 

 peduncles into the central olfactory region. Besides these, (1) the 

 inner olfactory tract is very clearly shown in the carp's brain, 

 [ol.i^ fig. 1, 2, 3). It consists of a compact bundle of about 20 

 large fibres which enter the olfactory nerve. Passing backwards to 

 the interlobular ridge these fibres cross each other i, and turn 

 upwards into a small cluster of cells in front of the middle bundle 

 of the hemispheral group. Whether they terminate here or pass 

 further backwards is doubtful. (2) Arising in the centre of the ol- 

 factory region and passing backwards, parallel with the former, is 

 an outer olfactory tract, forming a true commissure, which I 

 have designated the olfactory commissure [o.cm fig. 1 and 2) as it 

 unites the olfactory lobes. This is a larger bundle than the inner 

 tract and contains numerous fine fibres. It reaches the median line 

 somewhat below the inner tract. Its fibres scatter in the olfactory 

 lobes. (:?) The upper bundle of the olfactory group cm"' might readily 



1 Professor Gudden, in course of a private conversation, objected to the 

 use of the word »chiasraa« in this connection on the ground that liere there is 

 simply a crossing of two nerve roots from one side of tiie brain to the other 

 like that of the IV nerve, for example , to which the term chiasma is never 

 applied. Acting upon this suggestion I have not used the word. 



