CENTRAL NERVOUS SYSTEM IN VERTEBRATE ANIMALS. 
931 
Microscopic Anatomy of the Brain. 
Lobi Olfactorii. 
With the exception of the wings and of the tuberculum impar, the other parts of 
the brain have very nearly the same structure as in the ordinary Teleostean Fishes. 
The Mormyridce belong to that division of the Teleostei in which the olfactory lobes 
are situated at the extremity of a long peduncle far in advance of the anterior end of 
the brain and very near to the olfactory organ. 
They are fusiform in shape and are placed near the anterior extremity of the 
olfactory peduncle like a bead on a string, and the olfactory nerve pursues a short 
course before plunging into the sense organ. 
The structure of the olfactory lobes resembles that of the corresponding lobe in 
Mugil cephalus ; on the outside is seen a layer of the fibres which go to form the 
olfactory nerve. Many of these fibres are broad and. bandlike, resembling the fibres 
of Bemak in the sympathetic nerves ; they surround the whole lobe with the exception 
of the broader end which is directed towards the brain and from which the peduncle 
emerges. Towards the inner side of this layer of fibres and mingled with them is a 
stratum of larger sized cells which occur sometimes in groups of eight or ten and 
occasionally singly. They resemble those figured in my paper on the brain of Teleostei,* 
The central part of this lobe is occupied by numerous nerve cells of the smallest 
category, which some writers consider to be nuclei, but which, in Fishes at least, are 
certainly cells if Max Schultze’s! definition of a cell is to be accepted. They are 
rounded or oval, sometimes fusiform or pear-shaped. The more circular ones measure 
from 0‘004 millim. to 0'005 millim. in diameter; the fusiform ones with a process at 
each end measure about 0‘005 millim. by 0‘0067 millim. The rounded cells are 
occasionally seen to give off processes. These small nerve cells occupy a space the basis 
of which is a granular material in which numerous fibiillse are seen to ramify. The 
fibres of the olfactory commissure, on their entrance into the lobe, go directly into this 
central part; each fibre appears to be composed of an axis cylinder with a very small 
medullary sheath; they are smaller in diameter than the fibres of the olfactory nerve. 
The layers of the olfactory lobe are arranged here as in M. cephalus. The fibres 
of the olfactory nerve are outside and in front, the larger cells come next, and the 
smaller cells with the fibres of the olfactory peduncle occupy the centre and the 
posterior part, thus confirming the comparison of the structure of this lobe in the 
Mammalia with that of the corresponding lobe in Teleostei, which I made in the case 
of M. cephalus.\ 
* Phil. Trans., 1878. 
f U. Muskelkorper nnd das was man eine Zelle zu nennen habe. Arcliiy f. Anatomie, 1861, 
$ Loc. cit., p. 7o0, 
