A rather important element in the structure of animals is the “elastic ligament,” which is found in the back of the neck and other parts of the body, especially about the spine. It is made of a vast number of fibres of variable shape and length, branching and communicating, arranged generally in bundles, and remarkable for containing very few vessels, and no nerves at all. At Fig. 14 may be seen an example of elastic ligament, popularly called “paxwax,” taken from the neck of a sheep. The white fibrous tissue by which all the parts of the body are bound together is seen at Fig. 10; and at Fig. 11 is a beautiful example of the “ultimate fibres” of the crystalline lens of a sturgeon’s eye. The muscles of animals are of two kinds, the one termed the striped, and the other the unstriped. Of these, the latter belongs to organs which work independently of will, such as the stomach, etc., while the former belongs to those portions of the body which are subject to voluntary motion, such as the arm and the leg. The unstriped muscle is very simple, consisting merely of long spindle-shaped cells, but the striped or voluntary muscle is of more complex construction. Every voluntary muscle consists of myriads of tiny fibres, bound together in little bundles, enveloped in a kind of sheath. Fig. 24 is an example of this muscular fibre, taken from beef. When soaked in spirit, it often splits into a number of discs, the edges of which are marked by the transverse lines. A fibre of nerve is drawn at Fig. 23, and is given for the purpose of showing the manner in which the nerve is contained in and protected by its sheath, just like a telegraph-wire in its coverings. Just above is a transverse section of the same fibre, showing the same arrangement from another point of view, and also illustrating the curious phenomenon, that when nerve-fibres are treated with carmine the centre takes up the colouring matter, while the sheath remains white as before. The best way of studying nerves is to decapitate a frog, and cut off a piece of one of the nerves, which, like fine silk threads, come out between the joints of the spine inside the abdomen. By careful teasing out it is easy to obtain preparations showing all the above points, and, in addition, the folding-in of the internal sheath which correspond to the insulators of a telegraph-line.