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THE NERVOUS SYSTEM. 273

of which passes obliquely to a muscular fibre. Each muscular fibre
receives one or more nerve-terminals or end-plates. Most authorities
claim that at this point the medullary or white substance terminates,
and the neurilemma or primitive sheath (sheath of Schwann) becomes
continuous with the sarcolemma of the nuiscular fibre ; others state that
it (the medullary sheath) terminates immediately after passing through
the sarcolemma. Ranvier says that it is the nucleated sheath of Henle,
and not the neurilemma, which is continuous with the sarcolemma.
After the axis-cylinder passes through the sheath of the muscular fibre,
it divides and subdivides into numerous fibrillae, forming a network
Fig. 134.

Muscular Fibres of Lareria wrWis, with the terminations of nerves: n, seen in profile; P, P, the
nerve-end plates; 5, S, the base of the plate, consisting of a granular mass with nuclei; 6. the
same as seen in looking at a perfectly fresh fibre, the nervous ends being probably still excitable
(the forms of the variously-divided "plate can hardly be represented in a woodcut by sutiiciently
delicate and pale contours" to reproduce correctly wliat is .seen in nature); c, the same as seen two
hours after death from poisoning by curare.
which is imbedded in a more or less granular pale substance, usually
containing a number of oval nuclei having bright nucleoli. The sub-
division of the nerve-fibres, the granular substance, and the oval nuclei
forms the end-plafes, which usually have only one fibre terminating in
them, though occasionally there are two.

The Cranial Nerves.
The cranial nerves consist of one of the two divisions of the cerebro-
spinal system, receiving their name (cranial) from their origin within
the cranial cavity, with the exce])tion of the spinal accessory, which
originates, in part, out.'^ide the brain-ca.'^e, though this portion passes into
the cranium at the foramen magnum, and passes out in company with
its accessory portion through the posterior lacerated foramen.
A cranial nerve has two origins, superficial and deep : the first is
that portion of the nerve which can be traced to the circumference or
periphery of the brain ; while the deep origin is in relation with the
deeper structure of that organ.
The cranial nerves (Fig. 135) pass out of the brain-case through the
foramina in the cranial bones at the base of the skull. Internally they
Vol. 1.-18