Bones of the Leg.

In the upper part of the leg (see Fig. 64, A) is a single bone, the thigh bone or fe'mur. This corresponds in position to the humerus of the arm, but it is longer and stouter than the latter; in fact, it is the longest bone in the body. The skeleton in the calf of the leg consists of two bones, tib'i-a and fib'u-la, which have a position similar to that of the radius and ulna. The tibia is on the inner or great-toe side and is much larger than the slender fibula. At the kneejoint one can feel a flat piece of bone, more or less circular in outline, called the kneecap or pa-tel'la. When one extends the knee and rests the heel on the floor, the kneecap can be easily moved about over the kneejoint. There are seven tar'sal bones in the ankle, which like the carpals have a somewhat cubical form. They are, however, larger and less movable than the eight carpal bones of the wrist. One end of the arch of the foot rests upon the heel bone, the largest of the ankle bones. The arch is completed by the other tarsal bones, and by five rather slender met-atar'sals (Greek meta = beyond +tarsós ankle). The great toe has two, and each of the other toes three phalanges, making the same number of bones in the fingers and toes.

2. THE SKELETON OF THE NECK AND TRUNK

The Spinal Column. The erect position of the adult human body is maintained by a column of bones called vertebræ (Latin vertere: to turn, so called because these bones may be turned more or less on each other). The spinal column can be felt through the skin behind the neck and down the middle of the back.

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In the neck region are seven bones called cer'vi-cal vertebræ (Latin cervix neck); twelve dor'sal vertebræ carry the twelve pairs of ribs; and in the loins are the five large lum'bar vertebræ (Latin lumbus = loin). Below the lumbar bones is a single bone called the sa'crum. When one examines it, however, four ridges and four pairs of holes are

FIG. 64. Bones of Left Arm (B) and of Leg (A) together with Bones of

Girdles.

evident, which indicate the regions where the five separate vertebræ that are found in the sacrum of a child have grown together. Posterior to the sacrum in a child's skele

side view, showing curves.

S

= sacrum.

B = dorsal view, showing width of vertebræ. C = coccyx.

C. 1-77 cervical vertebræ.

D. 1-12 12 dorsal vertebræ.

=

sp spinous process.

tr = transverse process.

ton are four bones, which in the adult become united in one. From a fancied resemblance to a cuckoo's bill, this part of the spinal column is called the coc'cyx (from Greek, meaning cuckoo). Hence, in the spinal column of a child there are thirty-three separate bones; in that of an adult, twenty-six including sacrum and coccyx.

ar.....

B

sp

A

The Structure of a Vertebra. -The vertebræ are among the most irregular bones of the body. In general one may say that each consists of two parts; namely, a mass of bone called the centrum or body, and a bony arch with seven irregular processes. To this region of the vertebra is given the name neu'ral arch, because it helps to inclose the neural or spinal cord. The centrum is on the ventral side of the spinal column; circular B in outline, it is flattened above and

A

FIG. 66.

side view.

top view.

=

n =

ar articular process.

=

b= body or centrum.

neural ring (containing spinal cord).

sp= spinous process.

tr =

transverse process.

below, and on these surfaces are pads of cartilage that allow the vertebræ, to a certain extent, to turn and bend on each other. The weight of the body is supported by the body of the vertebra.

From the neural arch, as already stated, project seven processes. One of these is the spi'nous process, which can be felt in the middle of the back. It is this succession of processes that has suggested the name spinal column. Two lateral processes extend from the side of the neural arch, and to these processes the ribs are attached in the dorsal region of the spinal column. The other four projections from the arch of the vertebra are called ar-tic'u-lar processes; two of them face dorsally, the other two ventrally. Since they