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AREOLAE TISSUE, TENDONS, AND MUSCLES. 159
deep fascia, which form tlieir sheaths. The sheaths not only enclose
the individual fibres composing the bundles, but the entire tendon.
This latter covering is called the theca.
The fibres which make up a tendon are arranged parallel with each
other, and have an undulating course. Occasionally the fibrous bun-
dles send oft' fasciculi, some running forward and others backward,
interlacing with each other. The bundles proper, however, do not
subdivide, but keep intact from one extremity to the other.
The connective-tissue cells of tendons, called tendon-cells, are arranged
in parallel rows (Fig. 79), and follow the line of the fibrous bundles
composing the tendon. They are so closely approximated that in a
longitudinal section they have a stellate appearance, due to compression
of the cells and the elongated processes characteristic of all connective-
FiG. 79.

Tendon of Mouse's Tail, stained with logwood, showing chains of cells between ilie tendon-bui dies
(175 diameters).
tissue cells, which protrude from them, uniting one cell to another. These
cells are minute protoplasmic bodies, thicker in the centre than at the cir-
cumference, and contain a round or oval nucleus with several nucleoli.
Tendons are found connected with muscles at either terminal extrem-
ity or between the two bellies of the same muscle. Their fibres usually
run continuously with those of the muscle, but they may join the mus-
cle at an angle. When the tendinous fibres unite with the muscular
fibres end to end, the tendon is subdivided into as many fibres as there
are fibres in the muscle to which it is united. Adherence to this law is
so uniform that the fibres of the tendon seem to be but a continuation
of those of the muscle. A close examination, however, of the muscular
extremity of the fibres of the tendon will show that they suddenly end
on coming in contact with the truncated extremity of the muscle-fibre.
The sheaths, formed by fasciculi from the deep fascia, which enclose
the bundles of fibres forming the tendon, pass from the tendon-bundles
to the muscular fasciculi, and are lost by overlapping the similar sheaths
which enclose the muscular fibres, they all being continuous.
Where the fibres of the tendon are obliquely united to those of the
muscle the small tendinous bundles are given off laterally just at their
point of union, and extend between or over the muscular fibres, but
their sheaths are lost in the muscle in a manner precisely similar to the
union of the parallel fibres.
Muscular Tissue.
Muscular tissue is made up of fibres collected into distinct and sepa-
rate masses. By means of this tissue all the active movements of the