105. The LOWER EXTREMITIES contain sixty bones--the _Femur_, (thigh-bone;) the _Pa-tella_, (knee-pan;) the _Tibi-a_, (shin-bone;) the _Fibu-la_, (small bone of the leg;) the _Tarsus_, (instep;) the _Met-a-tarsus_, (middle of the foot;) and the _Pha-langes_, (toes.)

106. The FEMUR is the longest 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-tensor_ 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.

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.

[Ill.u.s.tration: 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.]

[Ill.u.s.tration: Fig. 18. 1, The tibia. 5, The fibula. 8, The s.p.a.ce 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.]

Explain fig. 17. Explain fig. 18.

111. The METATARSAL bones are five in number. They articulate at one extremity with one range of tarsal bones; at the other extremity, with the first range of the toe-bones.

[Ill.u.s.tration: Fig. 19. A representation of the upper surface of the bones of the foot. 1, The surface of the astragulus, where it unites with the tibia. 2, The body of the astragulus. 3, The calcis, (heel-bone.) 4, The scaphoid bone. 5, 6, 7, The cuneiform bones. 8, The cuboid. 9, 9, 9, The metatarsal bones. 10, The first bone of the great toe. 11, The second bone. 12, 13, 14, Three ranges of bones, forming the small toes]

[Ill.u.s.tration: Fig. 20. A side view of the bones of the foot, showing its arched form. The arch rests upon the _heel_ behind, and the _ball_ of the toes in front. 1, The lower part of the tibia. 2, 3, 4, 5, Bones of the tarsus. 6, The metatarsal bone. 7, 8, The bones of the great toe. These bones are so united as to secure a great degree of elasticity, or spring.]

_Observation._ The tarsal and metatarsal bones are united so as to give the foot an arched form, convex above, and concave below. This structure conduces to the elasticity of the step, and the weight of the body is transmitted to the ground by the spring of the arch, in a manner which prevents injury to the numerous organs.

111. Describe the metatarsal bones. Explain fig. 19. What is represented by fig. 20? What is said of the arrangement of the bones of the foot?

112. The PHALANGES (fig. 19) are composed of fourteen bones; each of the small toes has three ranges of bones, while the great toe has but two.

113. The JOINTS form an interesting part of the body. In their construction, every thing shows the regard that has been paid to the security and the facility of motion of the parts thus connected together. They are composed of the extremities of two or more bones, _Carti-lages_, (gristles,) _Syn-ovi-al_ membrane, and _Liga-ments_.

[Ill.u.s.tration: Fig. 21 The relative position of the bones, cartilages, and synovial membrane. 1, 1, The extremities of two bones that concur to form a joint. 2, 2, The cartilages that cover the end of the bones. 3, 3, 3, 3, The synovial membrane which covers the cartilage of both bones, and is then doubled back from one to the other; it is represented by the dotted lines.]

[Ill.u.s.tration: Fig. 22. A vertical section of the knee-joint. 1, The femur. 3, The patella. 5, The tibia. 2, 4, The ligaments of the patella.

6, The cartilage of the tibia 12, The cartilage of the femur. * * * *, The synovial membrane.]

114. CARTILAGE is a smooth, solid, elastic substance, of a pearly whiteness, softer than bone. It forms upon the articular surfaces of the bones a thin incrustation, not more than the sixteenth of an inch in thickness. Upon convex surfaces it is the thickest in the centre, and thin toward the circ.u.mference; while upon concave surfaces, an opposite arrangement is presented.

112. Describe the phalanges. 113-118. _Give the anatomy of the joints._ 113. What is said of the joints? Of what are the joints composed? What is ill.u.s.trated by fig. 21? By fig. 22? 114. Define cartilage.

115. The SYNOVIAL MEMBRANE is a thin, membranous layer, which covers the cartilages, and is thence bent back, or reflected upon the inner surfaces of the ligaments which surround and enter into the composition of the joints. This membrane forms a closed sac, like the membrane that lines an egg-sh.e.l.l.

[Ill.u.s.tration: Fig. 23. The anterior ligaments of the knee-joint. 1, The tendon of the muscle that extends the leg. 2, The patella. 3, The anterior ligament of the patella, near its insertion. 4, 4, The synovial membrane. 5, The internal lateral ligament. 6, The long external lateral ligament. 7, The anterior and superior ligament that unites the fibula to the tibia.]

[Ill.u.s.tration: Fig. 24. 2, 3, The ligaments that extend from the clavicle (1) to the scapula (4.) The ligaments 5, 6, extend from the scapula to the first bone of the arm.]

116. Beside the synovial membrane, there are numerous smaller sacs, called _burs mu-cos_. These are often a.s.sociated with the articulation. In structure, they are a.n.a.logous to synovial membranes, and secrete a similar fluid.

115. Describe the synovial membrane. 116. Describe the burs mucos.

What is represented by fig. 23? By fig. 24?

117. The LIGAMENTS are composed of numerous straight fibres, collected together, and arranged into short bands of various breadths, or so interwoven as to form a broad layer, which completely surrounds the articular extremities of the bones, and const.i.tutes a capsular ligament. These connecting bands are white, glistening, and inelastic.

Most of the ligaments are found exterior to the synovial membrane.

118. The bones, cartilages, ligaments, and synovial membrane are insensible when in health; yet they are supplied with organic nerves, as well as with arteries, veins, and lymphatics.

_Observation._ The joints of the domestic animals are similar in their construction to those of man. To ill.u.s.trate this part of the body, a fresh joint of the calf or sheep may be used. After divesting the joints of the skin, the satin-like bands, or ligaments, will be seen pa.s.sing from one bone to the other, under which may be observed the membranous bag, called the capsular ligament. This is very smooth, as it is lined with the soft synovial membrane, beneath which will be seen the cartilage, that may be cut with a knife, and under this the rough extremity of the ends of the bones.

117. Of what are ligaments composed? What is the appearance of these bands? Where are they found? 118. With what vessels are the cartilages and ligaments supplied? How can the structure of the joints be explained?

CHAPTER VI.

PHYSIOLOGY OF THE BONES.

119. The bones are the framework of the system. By their solidity and form, they not only retain every part of the fabric in its proper shape, but afford a firm surface for the attachment of the muscles and ligaments. By means of the bones, the human frame presents to the eye a wonderful piece of mechanism, uniting the most finished symmetry of form with freedom of motion, and also giving security to many important organs.