942 
MR. A. SANDERS ON THE ANATOMY OP THE 
directed with their long axis towards the molecular layer, instead of parallel with it; 
and thirdly, the granular layer itself contains cells of various sizes instead of all being 
uniform in dimensions. 
Medulla Oblongata. 
We now come to the consideration of the medulla oblongata. This contains an 
extraordinarily developed tuberosity, which Marco sen* took to be the cerebellum, 
and which he was puzzled to find had not the histological character of that organ. 
That it is not the cerebellum is certain ; what its real homology is will appear presently. 
In the meantime we can turn our attention to its minute structure. A reference to 
the figure (fig. 1) shows that it is an immensely developed tuberosity of a rounded 
shape placed immediately above the medulla oblongata and behind the cerebellum. It 
appears as a new development superadded to the usual elements of the Teleostean 
brain. It may be denominated for the present “ Tuberculum Impar.” 
A section, either longitudinal or transverse, shows that six layers from outside 
inwards may be distinguished by the different degrees in which they absorb the colour 
of the staining fluid. 
The first layer consists of small cells which become deeply coloured by the staining 
fluid. 
The second layer contains sections of obliquely directed bundles of nerve fibres. 
The third is a smoothly-granular layer which does not become so highly coloured as 
the outside, but which shows faint indications of radial striation. 
The fourth layer is a narrow stratum of variously-sized cells which become intensely 
coloured by the staining fluid. 
The fifth layer is occupied by a complex of medullated fibres, which form a com¬ 
plicated felt-like mass of intricate texture. 
The sixth layer exists only at the anterior end of the tuberculum impar, and con¬ 
sists of finely granulated matter. This is replaced at the posterior end by a circular 
hollow space which seems a mere gap in the tissue, and is not a ventricle properly 
speaking, since it is not lined by epithelium. 
Further inspection shows that the first or outer layer is not continuous throughout. 
Behind, it is deficient on the dorsal surface, the layers of each side ending within a 
short-distance from each other in a club-shaped termination (fig. 8), but towards the 
anterior end of the tuberculum impar they meet in the mid line (fig. 7), while quite at 
the front of that tubercle they are continuous with a part (fig. l) which is intercalated 
between the cerebellum and the tubercle in question. Both in the club-shaped dorsal 
termination at the posterior end of this layer, and at the anterior end, where the 
layers of the two sides meet in the mid line, the thickness is increased by the intro¬ 
duction of a new material consisting of a granular basis through which numerous cells 
of a very large size are interspersed, and the portion which is intercalated between 
* Loc, cit, 
