STRUCTURE OE THE BRAIN" IN RODENTS. 
729 
marginal aspect of the brain in its anterior regions—a region proved by Perrier to 
have motor endowments. In the Rat, on the other hand, this fasciculus is brought 
into relationship not so much with the motor cortex as with the cortex of the occipital 
pole, with which it has most extensive connexions. No doubt need be entertained 
upon these facts after a careful examination of horizontal and vertical sections of the 
frozen brain of these animals, and by dissection and teasing out of these structures. 
In vertical sections I have repeatedly succeeded in tracing the posterior commissural 
fasciculus upwards towards the projection system above, and have teased out, by 
means of a dissecting needle, the whole of its course from the anterior commissure 
to the brush-like head, leaving it a compact band of fibres entirely separated from the 
surrounding structures. 
The olfactory lyre .-—This is a structure which I have ventured to name by what 
appears a very appropriate term when its configuration is thoroughly understood—it 
has up to the present been entirely overlooked in descriptions of the olfactory apparatus. 
Meynert distinctly states, when describing the posterior extensions from the anterior 
commissure in his classical work on the brain of Mammals,* that the fasciculus passes 
“uninterruptedly through the corpus striatum.” This statement is, however, un¬ 
doubtedly an error, and it requires but a careful examination of vertical sections through 
this commissural tract in the Rabbit or a dissection of the fresh brain of the Rat or 
Rabbit to show not only that such is not the case, but that Meynert and others must 
have entirely overlooked here a structure which is most peculiar and important in its 
bearings. Vertical sections through the fresh brain of the Rabbit show very distinctly 
oval fasciculi of no mean size separating the strands of the posterior olfactory band, 
largest and most numerous near the auterior commissure (Plate 49, fig. 11, G). They 
consist of divided medullated fibres, which distinctly traverse the structure of the 
olfactory fasciculus from the portion of the striate body lying in front to that lying 
behind the commissure. In passing through the olfactory fasciculus a very apparent 
increase in the size of this tract is occasioned by this separation of its strands, so that a 
great oval enlargement characterises the earlier portion of this fasciculus in the Rabbit. 
A dissection of the brain of the Rat will indicate still more readily the nature of the 
structures here exhibited. Such a dissection will be described in detail further on—let 
it suffice here to state that by this method we expose a series of delicate fasciculi of 
medullated fibres passing from the posterior olfactory band forwards parallel to the 
central olfactory fasciculus. In part, these fibres traverse the structure of the olfactory 
band at right angles to its course, passing thus into the corpus striatum behind it, 
whilst others attached to the anterior margin of the same band curve inwards to 
accompany the rest of its fibres across the commissure. In passing forwards these 
fibres form a delicate floor or dissepiment betwixt the structure of the corpus striatum 
proper and that portion of the same ganglion which forms the olfactory area. This 
delicate sheet of medullated strands occupies a triangular space bounded internally by 
* Stricker’s ‘Handbook,’ Sydenham Soc. Trans. 
5 A 2 
