those which live in forests against a falling bough. They are passive creatures, mostly nocturnal in their habits, and their skeleton is strengthened in some parts in relation to its armour and its office. [Illustration: SKELETON OF THE ARMADILLO.] Thus the spine of the second vertebra is tall and compressed, and reaches backwards over those of the third and fourth vertebræ, and it coalesces with them. The bodies of these vertebræ also join more or less solidly, and there are no (or very minute) spines on the last three cervical vertebræ. This gives a strange appearance to the skeleton, which is increased by the length of the spine of the first vertebra of the back (dorsal). In order to support the back shield, the projections from the back bones are greatly developed, and two side processes stand out on either side of the spinous one. Moreover, there is much fixity between the last dorsal and lumbar vertebræ, and the strong and long sacrum beneath the last shield is formed by the junction of the back bones of the root of the tail with the true sacral vertebræ. Finally, the transverse processes of some of the upper tail vertebræ are united to the pelvic bones. There is a corresponding strengthening of the chest, and a broad flat first rib accompanies an expanded condition of the upper part of the breast bone; and this bone is jointed with bony sternal ribs, which unite on the side of the chest with the ordinary ribs of the spine. [Illustration: SKULL OF THE ARMADILLO.] As they are rapid burrowers, the limbs are fashioned with a view of favouring this kind of life, the general skeletal peculiarities of the Edentata being more or less preserved at the same time. They have a collar bone, and the blade bone is long, rather narrow, and has a tall, long spine, and a kind of offshoot from the back edge. The humerus of the arm is short and robust, strongly marked by ridges and depressions for the great muscles of the shoulder and chest, and the fore-arm is characterised by the disproportionate size of its two bones. The ulna has a very long and stout elbow process (olecranon) for the attachment of the muscles, which can force the hand strongly on to and into the earth, and drag it out, and its length makes the whole bone twice as long as the radius. The thigh bone has a strong crest, arising from the great trochanter, and extending downwards nearly the whole length of the bone; moreover, the great trochanter has a large process on the middle of its outer edge. The bones of the leg are broad, arched, and united at both ends, and the heel bone reaches far back, in order to give strength to the squatting position taken up when the animal is burrowing. The eye is placed rather high in the head, is protected above by the outer edge of the head armour, and by some small surrounding scales. It looks as a rule outwards. The lower jaw is long, and has a back angle, sometimes of some size; the cheek bone unites to the temporal bone, and the arch is complete.