r watch the motions of the eye. How rapid, how delicate, how
complicated, and yet how accurate, are the motions required! Think of
the endurance of such a muscle as the heart, that can contract, with a
force equal to sixty pounds, seventy-five times every minute, for
eighty years together, without being weary."

_Note._ It would be a profitable exercise for pupils to press their
fingers upon prominent muscles, and, at the same time, vigorously
contract them, not only to learn their situations, but their use; as
the one that bends the arm, 14, fig. 46.

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How is this illustrated? 172. Do all joints require the same number of
muscles, when called into action? How many are called into action in
the movement of the elbow? What is their office? What is said of the
movement of the ball and socket joint?

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[Illustration: Fig. 46. An anterior view of the muscles of the body. 1.
The frontal swell of the occipito-frontalis. 2, The orbicularis
palpebrarum. 3, The levator labli superioris. 4, The zygomaticus major.
5, The zygomaticus minor. 6, The masseter. 7, The orbicularis oris. 8,
The depressor labli inferioris. 9. The platysma myodes. 10, The deltoid.
11, The pectoralis major. 12, The latissimus dorsi. 14, The biceps flexor
cubiti. 15, The triceps extensor cubiti. 16, The supinator radii longus.
18, The flexor carpi radialis longior. 19, The flexor communis digitorum.
20, The annular ligament. 21, The palmar fascia. 22, The obliquus
externus abdominis. 26, The psoas magnus. 27, The adductor longus. 28,
The sartorius. 29, The rectus femoris. 30, The vastus externus. 31, The
vastus internus. 32, The tendon patellae. 33, The gastrocnemius. 34, The
tibialis anticus. 36, The tendons of the extensor digitorum communis.]

[Illustration: Fig. 47. A posterior view of the muscles of the body. 3,
The complexus. 4, The splenius. 5, The masseter. 6, The sterno-cleido
mastoideus. 7, The trapezius. 8, The deltoid. 10, The triceps extensor.
13, The tendinous portion of the triceps. 14, The anterior edge of the
triceps. 15, The supinator radii longus. 17, The extensor communis
digitorum. 18, The extensor ossis metacarpi pollicis. 19, The tendons of
the extensor communis digitorum. 20, The olecranon process of the ulna
and insertion of the triceps. 21, The extensor carpi ulnaris. 22, The
extensor communis digitorum. 24, The latissimus dorsi. 25, Its tendinous
origin. 26, The obliquus ex