454 THE XER VOl 'S S 1 'S TEM. 



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 PI. XXX., Fig. i, on the left side, 

 and also in PI. XXXII. , Fig. 2, and in PI. XXXIII., Fig. 3, 

 surrounding the thalamic lobe (//z). 



Comparison of the Lobes of the Cerebron of the Blow-fly and of 

 the Cricket. Yiallanes 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 



I)|>< 'KIM H>.\ <>l 1'I.AIK XXIX. 



JM<:. !. A lateral oblique section of the criebmn, cut from above downwards and 

 behind forwards, represented diagrammatical!/. Seen from above and in front. 

 </, right antenna! ganglion ; a', left antennal nerve : /'/-, left brachimn ; c c, corpus 

 centrale ; f/, right pmcereliral lobe ; g, space occupied by the pyramidal ganglion ; 

 ///, left hemisphere, in section ; //, nodulus ; o s, lift optic peduncle ; /'', left 

 italiecula. The shaded portions jf the central cavity represent its floor and the 

 upper surfaces of the trabecula. 1 . 



1 !.. j. A '-mi diagrammatic n-pirscntation of the ceiebrun of the fly, seen From 

 above and in front, showing the principal bundles of parallel fibres : itnt, antennal 

 nerve ; c, crus : t, inferior commissure of the mesoci-icbron : i.v, maxillary nervi-s ; 

 o, nerve to ocelli ; <r, cesophageal canal ; o s, optic peduncle ; /;', trabeculrc. 



