CENTRAL NERVOUS SYSTEM IN VERTEBRATE ANIMALS. 
751 
vacuities of the mammalian cerebrum, but actually injected one of them, — a fact 
which demonstrates that Stieda’s idea that they are artificial productions is erro- 
neous ; besides, Bevan Lewiss (84) also shows that they are real structures. The inner 
surface of these spaces is rendered smooth by an agglomeration and close apposition of 
the granules of the neuroglia, as in the olfactory lobes. 
The cells above described occupy a position intermediate between the small cells on 
the periphery and the central part of the lobes, which is occupied by white medullary 
fibres ; these fibres converge towards the postero-inferior angle, where they form a 
medullary cord. They are comparable to the “ corona radiata” of the cerebrum ; they 
pass downward and backward to be lost in the anterior end of the hypoarium. 
The cells become much less numerous in passing towards the centre of these lobes 
and are seldom found in the “ corona radiata those that do occur, however, have an 
elongated shape (fig. 16, d.), both protoplasm and nucleus appearing as if they had 
been pressed out by the surrounding fibres. The neuroglia, which occupies a large 
part of these lobes, is composed of a granular substance, in which extremely fine fibres 
ramify in all directions, forming a network uniting together the smaller cells above 
described. The transverse commissure which connects the lobe of one side to that of 
the other is formed of two bundles of fibres placed one behind the other ; the anterior 
bundle passes on each side forward into the anterior part of each lobe, and is lost in 
the walls of the fissure between the two lobes, while the posterior bundle passes more 
directly into the central parts. 
It will be seen that the structure of these lobes differs considerably from that of the 
lobi olfactorii. Here, there are no incipient glomeruli olfactorii, neither are there cell- 
like swellings of the nerve-fibres, nor a central group of cells ; but these bodies are 
more dispersed, are mostly of a different character, and are collected more towards the 
circumference. Thus, histological investigation does not support the opinion of some 
of the older anatomists, that these tuberosities homologise the bulbi olfactorii. The 
crura of the lobi olfactorii (fig. 1, ce.) pass from the posterior end of those lobes in a 
curved manner to the posterior end of the cerebral lobes, crossing over the fibres of the 
“corona radiata;” they cross these fibres, but have no direct communication with them, 
but continue their course into the posterior lateral lobule of the cerebrum, where they 
are lost. 
Tectum Lobi Optici. 
The structure of the tectum lobi optici differs in different parts of its extent ; taken 
at about the centre of its arch, it shows (fig. 18) seven layers, commencing on the 
outside. 
The first layer consists of finely granular neuroglia placed in immediate contact 
with the pia mater covering the tectum. 
The second layer consists of coarse fibres apparently transverse but really oblique, 
that is, going in a direction between transverse and longitudinal ; this layer contains 
sparsely distributed fusiform cells with their long axes placed radially. 
MDCCCLXXVIII. 5 D 
