But so also do the necks of mammals vary very greatly _in length_, while all, without exception, are formed of seven joints, _only seven vertebræ_; a man, a whale, a giraffe, and a mouse possess each seven cervical vertebræ, different in form from the rest of the joints of the spinal column. We might say that in appearance a whale has no neck, but its seven neck joints are flat and close as seven cards or seven pennies, while those of the giraffe are extraordinarily prolonged; and in ourselves—well, of course, the reader will admit the perfection of symmetry in our own necks, and the seven joints, therefore, are precisely of the proper size. While the spine of a snake is ‘simple’ in respect of its joints being all formed on the same plan, it is the reverse of simple in its wonderfully complex structure. Professor Huxley, in his delightful lecture, said that ‘the most beautiful piece of anatomy he knew was the vertebra of a snake.’ Professor Owen thus anatomically describes it: ‘The vertebræ of serpents articulate with each other by eight joints, in addition to those of the cup and ball on the centrum; and interlock by parts reciprocally receiving and entering one another, like the joints called tenon and mortice in carpentry’ (_Anatomy of the Vertebrates_, p. 54). [Illustration: Front and back view of a vertebra.] Bearing in mind that each of these highly complicated joints supports a pair of moveable ribs, and that the ends of these ribs are connected by muscles with the large stiff scutes or scales crossing the under surface of the body (see illustrations, p. 193), which move with the ribs, one foot-like scale to each pair, we comprehend how snakes exceed millipedes in the number of their _limbs_, if not true legs, and how they excel the insect also in variety of movement. Those ‘ball and socket’ joints admit of free lateral flexion, and every variety of curvature—‘_the utmost pliancy of motion_,’ to repeat the words of Rymer Jones; and also of that surprisingly independent motion which enables the constrictors to surpass even the _Bimana_ (except practised experts) in doing _several things at once_. Thoughtful persons who can contemplate this wondrous organization with due reverence, and witness it in activity—as we admiringly observe the works of a watch in motion—will forget to censure those who supply food to this piece of animated mechanism, and even pardon a hungry little snake for so expertly securing three birds at once. Think of 300 back-bones and 300 pairs of legs, all requiring wholesome exercise. Some snakes have 300 pairs of ribs—each pair capable of independent motion, and articulated with that complex spine; and each pair moving together, and carrying along with them a foot in the shape of a broad ventral scale. ‘This scutum by its posterior edge lays hold of the ground,’ says Sir Everard Home, ‘and becomes a fixed point whence to set out anew.’