748 
MR. A. SANDERS ON THE ANATOMY OF THE 
arch is given off from its posterior end, while the branch which joins the facial root 
of the trifacial comes off from its anterior side. 
Thus we have here a corresponding nerve given off from two distinct sources in 
allied species, so that it seems not beyond the bounds of possibility, with such varying 
elements (evolution being granted), that the branchial divisions of the vagus should 
be detached from that trunk, and absorbing the branch of the acusticus to the first 
branchial arch should become developed in the higher Vertebrata as the glosso- 
pharyngeal ; and, on the other hand, that the facial division of the trifacial should 
become detached from that origin, and attach itself entirely to the anterior cord of the 
same branch of the acusticus ; the two halves of the latter being separated. Then the 
communicating twig between the glossopharyngeal and the facial remains as evidence 
of their former union. 
Microscopic Anatomy of the Brain. 
Lobi Oifactorii. 
The lobi oifactorii (fig. 1, ol.) consist essentially of three layers. Of these the external 
is thicker in front, and is formed by the fibres of the olfactory nerve (fig. 1, n. 1), which 
on entering diverge in all directions and form a sort of envelope for the anterior part 
of the lobe. More internal comes a layer of finely granular neuroglia, which surrounds 
on the upper, anterior, and lower sides a mass of small cells, which occupy the central 
and posterior part of the lobe, being separated from the hinder edge by a narrow 
stratum of fibres, which descend to the postero inferior angle, and pass out to form the 
commissure between this lobe and the cerebrum (fig. 15, ab.). 
The cells of the central group are small in size, resembling to a certain extent 
those of the cerebrum. Many are oval or circular in outline, but generally they are 
more or less pear-shaped. Each cell has a nucleus of comparatively large size, which 
is invariably situated at the broader end of the cell ; the protoplasm or cell-contents 
occupy the narrower side, which terminates in a more or less blunt point, from which 
a single free fibril emerges. The nucleus contains a single spot-like nucleolus, situated 
near the centre, which occasionally shows symptoms of breaking up into its constituent 
granules. The total average length of these cells is 0 - 007 millim. or 0'008 millim., 
their diameter 0'004 millim. or 0 - 005 millim. ; the nuclei are generally round, or nearly 
so ; and their diameter averages 0'004 millim. 
Many of these cells occupy spaces in the neuroglia which probably correspond to 
the spaces surrounding the cells of the cerebrum described by Obersteiner (78) and 
Bevan Lewiss (84). Occasionally, nearly the whole of the cell projects into this 
chamber, but more generally only the broad end, so that the nucleus alone would 
be bathed in lymph in the latter case. The granules which to a great extent compose 
the neuroglia of the olfactory lobes become aggregated together, and form a smooth 
surface on the walls of these spaces ; they do not actually form an epithelial layer, but 
seem to be a rudimentary form of that structure. 
