The superior olivary nucleus gives off a small strand of fibers called the olivary pedicle which runs dorso-medially between the roots of the facial and abducent nerves, to the nucleus of the abducent nerve; there some of its fibers end, the remainder join the medial longitudinal bundle and run to the trochlear and oculomotor nuclei. The pedicle forms part of an auditory ocular reflex arc.
A small accessory nucleus, called the nucleus prceolivaris, is situated just a little ventral to the superior olivary nucleus; and a second one embraces the convexity of the nucleus olivaris superior, lying on the medial side of it. The latter is the nucleus semilunaris.
Nucleus of the Trapezoid Body (n. corporis trapezoidei).— This nucleus is deeply imbedded in the trapezoid body ventro medial to the superior olivary nucleus (Fig. 116). Its cell-bodies are scattered and, like the other nuclei of the olivary group, it forms a partial relay for the auditory path. This nucleus is peculiar; the fibers it receives terminate in the form of cup shaped discs, acustic cups, which are in direct contact with its cell-bodies (Heald).
2. The nuclei of the reticular formation contained in the pons are the n. centralis superior, n. centralis medius, n. centralis inferior and n. lateralis medius. All are microscopic. They are made up of large scattered cell-bodies whose axones, dividing T like, are both ascending and descending in direction (Tscher mak). We may divide these axones into two groups, a crossed and an uncrossed. The crossed fibers pierce the median plane and become longitudinal in the formatio reticularis near the ventricular gray matter and lateral to the root of the abducent nerve. At that point they bifurcate' and one branch runs up ward and the other downward. The descending branches of the crossed fibers (lateral reticulo-spinal tract) pass through the substantia reticularis grisea of the medulla and the lateral column of the spinal cord throughout its length; they end in the gray crescent in successive segments until exhausted near the end of the cord (Tschermak, Barker). The uncrossed fibers from the reticular nuclei enter the medial longitudinal bundle of the same side and there branch T-like. The descending
branches (anterior reticulo-spinal tract) run with this bundle into the anterior column of the spinal cord, through which some of them continue to the end. They occupy the outer side of the anterior funiculus and end in succession in the anterior columna of gray matter (Tschermak and Barker). Just what is the destination of the ascending branches of either group of fibers has not been determined. J. S. Collier suggests that these tracts from the reticular nuclei should be called the crossed and uncrossed ponto-spinal tracts (Brain, Vol. 24, 1901).
3. Nerve nuclei of the trigeminal nerve (nuclei nervi trigemini) are two in number. The genetic or motor nucleus of the fifth nerve (n. motorius) in the pons is a continua tion of the mesencephalic nucleus. It is rather close to the fourth ventricle in the extreme lateral part of its floor, under neath the locus cwruleus (Fig. 112). It extends as far down as the middle of the pons, where the whole group of axones passes forward into the motor root of the nerve. The dark ferruginous cells of the locus cxruleus form no part of the motor nucleus of the fifth and have no connection with either of its roots (Horsley). The pontine part of the motor nucleus of the trigeminal nerve is purely somatic, in that it supplies voluntary body muscles (soma-body). The mesencephalic nucleus is commonly considered a motor nucleus whose axones enter into the main motor root of the fifth (the masticator nerve); but its real nature is much in doubt (see p. 239).
Cortical Connection.—The nucleus receives motor fibers from the opposite pyramidal tract and perhaps from the cerebro pontal tracts of the same side; and sensory fibers terminate in it from the sensory root of the fifth nerve, and from the terminal nuclei of other common sensory nerves, through the medial longitudinal bundle and establish its reflex connections. Cerebello-tegmental fibers in the brachium conjunctivum also terminate in it; and the vestibular nuclei, connected with the cerebellum by the cerebello-tegmental fibers of the restiform body, send fibers to it, all of which bring coordinated reflex im pulses from the cerebellum.