ROBIE OTST THE AHATOMY OF THE OLFACTORY LOBES. 289 
olfactory lobes and tbe spinal cord arose from tbe outer anterior part 
of lobe, instead of from the inner as in the Bat, and became lost in 
the crura cerebri. 3rd. The olfactory commissure terminated in the 
inner anterior part of the lobes, the outer anterior part being occu¬ 
pied by the long bands just described. 
I may here add that an olfactory commissure is not confined to the 
mammalia. It undoubtedly exists in some fishes. At least 1 have 
found it well marked in the Mackerel (Scomber Scomber ), and occupy¬ 
ing a position similar to that already described (Fig. 2). As to the 
functions which these fibres may be considered to perform, we have 
already stated that the superficial fibres of communication between 
the olfactory lobes and the cerebrum may be regarded as conveying 
to the brain proper the impressions made on the olfactory lobes. The 
commissural fibres, no doubt, have the same function here as else¬ 
where, and serve to co-ordinate such impressions. 
The functions of the other fibres, however, are not so easily ex¬ 
plained. Those arising from the convexity of the commissure may, 
I think, be regarded as fibres passing from each olfactory lobe 
respectively to the opposite side of the cerebrum, thus crossing each 
other in their course. Constituting as they do only about one-fifth of 
the whole fibres of the commissure, and existing, so far as I could 
ascertain, in only one of the species examined, their function may be 
merely of a secondary nature, that of assisting in the co-ordinating 
action of the commissure. With regard to the fibres passing from 
the olfactory lobes towards the spinal cord, two views may be enter¬ 
tained ; either that they terminate in the spinal centres of locomotion 
or of respiration. In either case they would appear to constitute a 
reflex apparatus, whereby locomotion or respiration might be excited 
independently of cerebral action, an arrangement which must be re¬ 
garded as highly necessary, when we take into consideration the 
habits of these animals. 
DESCRIPTION OF FIGURES. 
/ 2 
Fig. 1 . —Section showing the arrangement of the deep bundles of nerve fibres in 
the olfactory lobes of the common Rat (Mus dccumanus.) 
Fig. 2. —Section showing the olfactory commissure in the lobes of the Mackerel 
(Scomber Scomber ). 
N. H. R.—1863. 
U 
