3. The vertebral column.—Make out that each of the bones [Pg 223] (vertebrae) which compose the vertebral column is really a ring, and that the whole column is therefore a bony tube. In this tube is enclosed the spinal cord, a backward continuation of the brain. Examine and draw vertebrae from the various parts of the column, and notice how they vary in shape and size. Compare vertebrae from (a) the neck, (b) the region of the chest (notice the attachment of the ribs), (c) the abdominal region, (d) the region of the hips (four united vertebrae; leave these for the present in position between the hip-bones), (e) the tail. 4. The ribs and sternum.—Examine the manner of attachment of the anterior (p. 217) pairs of ribs to the sternum or breast-bone. Some of the more posterior ribs are free at their ventral ends. 5. The bones of the fore-limb.—Examine the bones in order and make out: (a) the triangular shoulder-blade, (b) the single long bone of the upper arm (its upper, rounded end fitting into a socket in the shoulder-blade; its lower end forming, with the bones of the fore-arm, the elbow joint), (c) the two bones of the fore-arm (these lie side by side; notice the peg which makes it impossible for the hinged elbow-joint to be bent back beyond a straight line), (d) the small bones of the wrist, (e) the bones of the hand. 6. The bones of the hind-limb.—Notice that the limb as a whole is divided into parts—upper leg, leg, ankle and foot—which correspond to the divisions of the fore-limb. Make out: (a) that as the bone of the upper arm fits into a socket in the shoulder-blade, so the bone of the upper leg has a ball-shaped end which works in a socket of the hip-bone. Notice that the two hip-bones are joined together ventrally, and that they are fixed to the welded vertebrae of the hip-region. Does this give increased strength to the hind-limb? Identify: (b) the two bones of the leg (between knee and ankle) and notice that they differ from the corresponding bones of the arm in being fused together in the lower part; (c) the bones of the ankle, and (d) the bones of the foot.