454 THE NERVOUS SYSTEM. 
in front of these peduncles the following lobes may be dis- 
tinguished : the superior middle and frontal lobes of the meso- 
cerebron. Below the optic peduncle there is a considerable 
swelling, which may be termed the inferior lobe. In front of 
the middle and inferior lobes there is a hemispherical enlarge- 
ment, which I regard as the thalamic lobe. The relations of 
these lobes will be seen in Plate XXVIII. and Fig. 56. 
The Lateral Fissure.-—This is a very remarkable fissure which 
has somewhat the form of an inverted y; its upper limb is 
curved, and separates the frontal and middle lobes of the 
mesocerebron ; its two descending limbs embrace the thalamic 
lobe. The upper portion of the sulcus is merely a superficial 
furrow; but the anterior and posterior limbs, and the lower 
part of the upper limb, are very deep, and extend into the 
central cavity. The lateral fissure separates the thalamic lobe 
from the surrounding lobes of the mesocerebron, just as the 
Silvian fissure separates the Island of Reil from the surround- 
ing parts of the cerebrum of a vertebrate. Like the longi- 
tudinal fissure, it is filled by a process from the cellular cortex. 
It is well seen in section in Pl. XXX., Fig. 1, on the left side, 
and also in Pl. XXXII., Fig. 2, and in Pl. XXXIII., Fig. 3, 
surrounding the thalamic lobe (th). 
Comparison of the Lobes of the Cerebron of the Blow-fly and of 
the Cricket.—Viallanes terms the hemispheres protocerebral 
lobes, and gives the following description of these structures 
in the Cricket [185, Mem. 5]: ‘The protocerebral lobe is the 
most voluminous part of the brain; externally it is united with 
DEscRIPTION OF PLATE XXIX. 
Fic, 1.—A lateral oblique section of the cerebron, cut from above downwards and 
behind forwards, represented diagrammatically. Seen from above and in front. 
a, right antennal ganglion ; a’, left antennal nerve ; 4”, left brachium ; ¢ ¢, corpus 
centrale ; c/, right procerebral lobe ; g, space occupied by the pyramidal ganglion ; 
m, left hemisphere, in section; 7, nodulus; 0 s, left optic peduncle; 7“, left 
trabecula, The shaded portions of the central cavity represent its floor and the 
upper surfaces of the trabeculz, 
Fic, 2.—A semi-diagrammatic representation of the cerebron of the fly, seen from 
above and in front, showing the principal bundles of parallel fibres : a/, antennal 
nerve; ¢, crus; #, inferior commissure of the mesocerebron; 7, maxillary nerves ; 
0, nerve to ocelli; a, cesophageal canal; 0 s, optic peduncle ; ¢”, trabeculz. 
