est bone in the system. It supports the
weight of the head, trunk, and upper extremities. The large, round
head of this bone is placed in the acetabulum. This articulation is a
perfect specimen of the ball and socket joint.

107. The PATELLA is a small bone connected with the tibia by a strong
ligament. The tendon of the _ex-tens'or_ muscles of the leg is
attached to its upper edge. This bone is placed on the anterior part
of the lower extremity of the femur, and acts like a pulley, in the
extension of the limb.

108. The TIBIA is the largest bone of the leg. It is of a triangular
shape, and enlarged at each extremity.

109. The FIBULA is a smaller bone than the tibia, but of similar
shape. It is firmly bound to the tibia, at each extremity.

110. The TARSUS is formed of seven irregular bones, which are so
firmly bound together as to permit but little movement.

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104. How many ranges of bones have the phalanges? 105-112. _Give the
anatomy of the bones of the lower extremities._ 105. How many bones in
the lower extremities? Name them. 106. Describe the femur. 107.
Describe the patella. What is its function? 108. What is the largest
bone of the leg called? What is its form? 109. What is said of the
fibula? 110. Describe the tarsus.

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[Illustration: Fig. 17. 1, The shaft of the femur, (thigh-bone.) 2, A
projection, called the trochantar minor, to which are attached some
strong muscles. 4, The trochantar major, to which the large muscles of
the hip are attached. 3, The head of the femur. 5, The external
projection of the femur, called the external condyle. 6, The internal
projection, called the internal condyle. 7, The surface of the lower
extremity of the femur, that articulates with the tibia, and upon which
the patella slides.]

[Illustration: Fig. 18. 1, The tibia. 5, The fibula. 8, The space between
the two, filled with the inter-osseous ligament. 6, The junction of the
tibia and fibula at their upper extremity. 2, The external malleolar
process, called the external ankle. 3, The internal malleolar process,
called the internal ankle. 4, The surface of the lower extremity of the
tibia, that unites with one of the tarsal bones to form the ankle-joint.
7, The upper extremity of the tibia, upon which the lower extremity of
the femur rests.]

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Explain fig. 17. Explain fig. 18.

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111. The METATARSAL b