ME. J. L. CLAEKE ON THE INTIMATE STEUCTUEE OE THE BEAIN. 
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CHAPTEE II. 
(24) The little column of cells and longitudinal fibres seen at K', fig. 25, Plate X., 
lying at the side of the central canal and immediately behind the hypoglossal nucleus (J), 
increases in size as it ascends the medulla to constitute the so-called “ fasciculus teres .” 
Above the calamus scriptorius, on the floor of the fourth ventricle, it increases most 
rapidly, and rather suddenly, just in proportion to the decrease of the hypoglossal 
nucleus. Pig. 38, Plate XI. represents a transverse section of the floor of the ventricle 
at this level, on the left of the median line. J is the hypoglossal nucleus considerably 
diminished in size. Behind and overlying it is the “ fasciculus teres ” (K'), much 
increased in size, in consequence of the greater number of both the fibres and cells 
which it contains, the fibres for the most part forming a layer nearer its posterior 
surface. It is an oval or pyriform mass, and lies with its longer axis transversely inward 
and outward. On its inner side it tapers over the back of the hypoglossal nucleus, to 
join a small oval group of closely aggregated cells (T), which now makes its appearance 
along each border of the raphe ; and on the outer side it tapers under, or in front of, 
the oval group of cells (H) forming the inner portion of the vagal nucleus, which partly 
overlies it. Some of the fibres of the vagus nerve (y) appear to be connected with it, 
as they run along its lower border to the hypoglossal nucleus. The outer portion of 
the vagal nucleus is at t, and the slender longitudinal column at n. 
(25) A transverse section of the floor of the fourth ventricle a little higher up (on a 
level with the roots of the glossopharyngeal nerve) is represented in fig. 39, Plate XI. 
Plere we find that the hypoglossal nucleus has almost wholly disappeared, only a few 
small cells ( J, J'), belonging apparently to the anterior group, remaining in company with 
a few commissural fibres and nerve-roots (x). The dark oval group of nuclei (T) is much 
larger than in the preceding section, and on its outer side, on the surface of the ven- 
tricle, is the cut end of one of the striae medullar es (T v ). The “ fasciculus teres ” (K') has 
nearly doubled its size, and is connected by a curved band of fibres with the posterior 
nucleus ( i ) of the auditory nerve ; t is the outer portion of the glossopharyngeal nucleus. 
It is much smaller than the corresponding part of the vagal nucleus (fig. 38), and has 
diminished in proportion as the auditory nucleus (i) has enlarged. On the right of t, 
the group of cells constituting the inner nucleus of the glossopharyngeal nerve has 
altered a little in form, being somewhat club-shaped instead of oval. 
(26) In the central part of each lateral half of the medulla, and near the inner side 
of the caput cornu posterioris or grey tubercle (e, fig. 10, Plate VIII.), there is a pecu- 
liar group of large multipolar cells (U), precisely similar in appearance to those in the 
anterior cornu of the spinal cord. This is the lower part of a longitudinal column of 
cells, constituting the nucleus of the lesser root of the trigeminal or fifth cerebral nerve. 
Higher up in the medulla, on a level with the auditory nerve, it was pointed out by 
Stilling; but I have traced it much lower down — sometimes nearly as low as the level 
