Part 5 (1/2)

86. How are the ribs united to the sternum? 87. Describe the spinal column. 88. Give the structure of the vertebra. Where is the spinal cord placed? 89. What is placed between each vertebra? What is its use?

90. Another provision for the protection of the brain, which bears convincing proof of the wisdom and beneficence of the Creator, is the antero-posterior, or forward and backward curve of the spinal column.

Were it a straight column, standing perpendicularly, the slightest jar, in walking, would cause it to recoil with a sudden jerk; because, the weight bearing equally, the spine would neither yield to the one side nor the other. But, shaped as it is, we find it yielding in the direction of the curves, and thus the force of the shock is diffused.

[Ill.u.s.tration: Fig. 10. A vertebra of the neck. 1, The body of the vertebra. 2, The spinal ca.n.a.l. 4, The spinous process, cleft at its extremity. 5, The transverse process. 7, The inferior articulating process. 8, The superior articulating process.]

[Ill.u.s.tration: Fig. 11. 1, The cartilaginous substance that connects the bodies of the vertebr. 2, The body of the vertebra. 3, The spinous process. 4, 4, The transverse processes. 5, 5, The articulating processes. 6, 6, A portion of the bony bridge that a.s.sists in forming the spinal ca.n.a.l, (7.)]

_Observation._ A good idea of the structure of the vertebr may be obtained by examining the spinal column of a domestic animal, as the dog, cat, or pig.

91. The PELVIS is composed of four bones; the two _in-nom-i-nata_, (nameless bones,) the _sacrum_, and the _coccyx_.

92. The INNOMINATUM, in the child, consists of three pieces. These, in the adult, become united, and const.i.tute but one bone. In the sides of these bones is a deep socket, or depression, like a cup, called the _ac-e-tabu-lum_, in which the round head of the thigh-bone is placed.

90. What is said of the curves of the spinal column? What is represented by fig. 10? By fig. 11? How can the structure of the vertebr be seen? 91. Of how many bones is the pelvis composed? 92.

What is said of the innominatum in the child?

93. The SACRUM, so called because the ancients offered it in sacrifices, is a wedge-shaped bone, that is placed between the innominata, and to which it is bound by ligaments. Upon its upper surface it connects with the lower vertebra. At its inferior, or lower angle, it is united to the coccyx. It is concave upon its anterior, and convex upon its posterior surface.

[Ill.u.s.tration: Fig. 12. 1, 1, The innominata, (nameless bones.) 2, The sacrum. 3, The coccyx. 4, 4, The acetabulum. a, a, The pubic portion of the innominata. d, The arch of the p.u.b.es; e, The junction of the sacrum and lower lumbar vertebra.]

94. The COCCYX, in infants, consists of several pieces, which, in youth, become united and form one bone. This is the terminal extremity of the spinal column.

In the adult? Describe the acetabulum. 93. Describe the sacrum.

Explain fig. 12. 94. Describe the coccyx.

CHAPTER V.

ANATOMY OF THE BONES, CONTINUED

95. The bones of the upper and lower limbs are enlarged at each extremity, and have projections, or processes. To these, the tendons of muscles and ligaments are attached, which connect one bone with another. The shaft of these bones is cylindrical and hollow, and in structure, their exterior surface is hard and compact, while the interior portion is of a reticulated character. The enlarged extremities of the round bones are more porous than the main shaft.

96. The UPPER EXTREMITIES contain sixty-four bones--the _Scapu-la_, (shoulder-blade;) the _Clavi-cle_, (collar-bone;) the _Humer-us_, (first bone of the arm;) the _Ulna_ and _Radi-us_, (bones of the fore-arm;) the _Carpus_, (wrist;) the _Met-a-carpus_, (palm of the hand;) and the _Pha-langes_, (fingers and thumb.)

97. The CLAVICLE is attached, at one extremity, to the sternum; at the other, it is united to the scapula. It is shaped like the Italic _[s]_. Its use is to keep the arms from sliding toward the breast.

98. The SCAPULA is situated upon the upper and back part of the chest.