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THE NERVOUS SYSTEM. 271

which form iu themselves .small axis-cylinders without any membranes.
These unite and form larger axis-cylinders, finally taking on the neu-
rilemma or white sheath of Schwann, then the medullary envelope, the
fibres uniting into bundles.

The Peripheral End-organs.
The peripheral end-organs are divided into two classes, those of sen-
sation and those of motion.
The Peripheral End-organa of Sensory or Afferent Nerves.—Many
of these nerves terminate in fine plexuses or have free ends (as those
already described) under the final termination of the medullary nerve-
fibres, which are distributed to the mucous membrane, cornea, and skin.
Other terminations *are found in various organs of special sense and
function : amongst the most important of these are the Pacinian and
tactile corpuscles (see Anatomy of the Skin for description), the spheroidal
end-bulbs of Krause, hair-bulbs, and nerves ending in gland-cells.
The small spheroidal oid-bidbs of Krause, resembling to a certain
extent the Pacinian corpuscles, are found near the corneal margin of the
deeper layers of the conjunctiva (Fig. 131) of man and apes ; in other
animals they are cylindrical. These
have also been found in various parts Fig. 131.
of the skin and the mucous membrane
of the mouth. The spheroidal end-
bulbs are composed of polygonal cells t^:
d
and slightly granular substance, sur-
rounded or invested externally by a
connective-tissue capsule, which is a
continuation of the sheath of Heide
of the nerve-fibre, and internally by a
nucleated membrane which is a con-
tinuation of the primitive nerve-enve-
lope. Usually the axis-cylinder enters
the bulb devoid of the medullary
sheath, though occasionally it passes Knd-bulb from Uie lluman conjunctiva;
, 1 11 • 1 1 • • tj ", nucleated capsule; fc.core^the outlines
into the bulb with this covering. It of itscellsarenotseen;r,entennKtibre,
T
may enter undivided 1 or m several 1 branching, and its two divisions passing ^
•
• 1
'
^ to tenni.,ate in the core at d.
branches ; if the latter, the branches
twist and intermingle with each other before entering, making a
number of turns, finally dividing into fibrillse within the bulb ; these,
after making numerous convolutions, are ultimately lost within the
substance.
The Hair-bulbs contain terminations of fibres of the medullary nerves,
giving extreme sensitivity in cases where the hair is used as a sentinel, as
in the eyelashes and the whiskers of cats, dogs, and other animals.
Nerve-endings in the Gland-cells.
As by mental influences some glands can be excited to secretion,
nerve-fibres must be directly connected A^ith them. Pliiger claims