But if the fore-hand so greatly resembles a paw, compensation is made to the animal by the gift of the prehensile tail, which is very muscular, and the under surface is without hair near the end, so that the sensitive surface can touch and feel objects. They can feel, therefore, around them, and also above them, as they move along and lay hold of branches and hanging creepers without looking for them. The delicate sense of feeling depends on the nervous supply; and the power of clasping and holding on upon the bending or flexor muscles. A bony framework supports all these structures, and runs from the last bone of the sacrum to the tip, and consists of many separate vertebral bones placed in a long series. The first few bones which join on to the sacrum, and form the root of the tail, resemble the back-bone pieces, or vertebræ, to a certain extent. Each has a body, and also processes for jointing with the one before and behind, and a spine also. Besides these, there are two curious projections on the lower part of each body, which are called chevron bones, and are V-shaped, and their use is to allow the blood-vessels and nerves to pass along between them without being pressed upon. Towards the end of the tail the vertebræ become long and stout, and are united behind and in front, forming a broad bone, and without the joints, and the chevron bones are reduced to little rounded pieces of bone. Everything tends in this tail to ready, rapid, and forcible motion, and indeed so perfect an organ is it that when one of these Howlers is shot it always hangs to the tree by its tail, even if quite dead, and does not fall down until some hours afterwards, when the strong flexor muscles have relaxed. Therefore, writes a recent author, if fresh food is required, it is best to kill a Lagothrix (see page 171) in the Peruvian valleys, as hung meat soon becomes tainted. The Golden Howler, nevertheless, furnishes the principal animal food to the inhabitants of the banks of some of the rivers entering the Peruvian Amazon. They keep to the low lands and shores of the rivers, and are found moving from place to place in pairs. [Illustration: SECTION OF HEAD AND OF AIR SAC OF THE HOWLER. (From the _Cyclopædia of Anatomy and Physiology._)] [Illustration: UPPER PART OF BREAST-BONE AND COLLAR-BONES OF THE HOWLER.]