f the bones that concur in forming a joint. Its use is to
facilitate the motion of the joints by its smooth surface, while its
elastic character diminishes the shock that would otherwise be
experienced if this tissue were inelastic.

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36. Describe the adipose tissue. Where does this tissue principally
exist? Give observation in regard to the adipose tissue. 37. Describe
the cartilaginous tissue. What is its use?

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38 The OSSEOUS TISSUE, in composition and arrangement of matter,
varies at different periods of life, and in different bones. In some
instances, the bony matter is disposed in plates, while in other
instances, the arrangement is cylindrical. Sometimes, the bony matter
is dense and compact; again, it is spongy, or porous. In the centre of
the long bones, a space is left which is filled with a fatty
substance, called _mar'row_.

_Observation._ Various opinions exist among physiologists in regard to
the use of marrow. Some suppose it serves as a reservoir of
nourishment, while others, that it keeps the bones from becoming dry
and brittle. The latter opinion, however, has been called in question,
as the bones of the aged man contain more marrow than those of the
child, and they are likewise more brittle.

[Illustration: Fig. 5. A section of the femur, (thigh-bone.) 1, 1, The
extremities, showing a thin plate of compact texture, which covers small
cells, that diminish in size, but increase in number, as they approach
the articulation. 2, 2, The walls of the shaft, which are very firm and
solid. 3, The cavity that contains the marrow.]

39. The MUSCULAR TISSUE is composed of many fibres, that unite to form
fasciculi, each of which is enclosed in a delicate layer of cellular
tissue. Bundles of these fasciculi constitute a muscle.

_Observation._ A piece of boiled beef will clearly illustrate the
arrangement of muscular fibre.

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38. What is said of the osseous tissue? How is the bony matter
arranged in different parts of the animal frame? What is said of the
use of marrow? 39. Of what is the muscular tissue composed? How may
the arrangement of muscular fibre be illustrated?

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40. The MUCOUS TISSUE differs from the serous by its lining all
the cavities which communicate with the air. The nostrils, the
mouth, and the stomach afford examples. The external surface of this
membrane, or that which is e