(5) _Tail._--The absence of a tail in man is popularly supposed to constitute a difficulty against the doctrine of his quadrumanous descent. As a matter of fact, however, the absence of an external tail in man is precisely what this doctrine would expect, seeing that the nearest allies of man in the quadrumanous series are likewise destitute of an external tail. Far, then, from this deficiency in man constituting any difficulty to be accounted for, if the case were not so--i. e. if man _did_ possess an external tail,--the difficulty would be to understand how he had managed to retain an organ which had been renounced by his most recent ancestors. Nevertheless, as the anthropoid apes continue to present the rudimentary vestiges of a tail in a few caudal vertebræ below the integuments, we might well expect to find a similar state of matters in the case of man. And this is just what we do find, as a glance at these two comparative illustrations will show. (Fig. 15.) Moreover, during embryonic life, both of the anthropoid apes and of man, the tail much more closely resembles that of the lower kinds of quadrumanous animals from which these higher representatives of the group have descended. For at a certain stage of embryonic life the tail, both of apes and of human beings, is actually longer than the legs (see Fig. 16). And at this stage of development, also, the tail admits of being moved by muscles which later on dwindle away. Occasionally, however, these muscles persist, and are then described by anatomists as abnormalities. The following illustrations serve to show the muscles in question, when thus found in adult man. [Illustration: FIG. 15.--Sacrum of Gorilla compared with that of Man, showing the rudimentary tail-bones of each. Drawn from nature (_R. Coll. Surg. Mus._).] [Illustration: FIG. 16.--Diagrammatic outline of the human embryo when about seven weeks old, showing the relations of the limbs and tail to the trunk (after Allen Thomson), _r_, the radial, and _u_, the ulnar, border of the hand and fore-arm; _t_, the tibial, and _f_, the fibular, border of the foot and lower leg; _au_, ear; _s_, spinal cord; _v_, umbilical cord; _b_, branchial gill-slits; _c_, tail.] [Illustration: FIG. 17.--Front and back view of adult human sacrum, showing abnormal persistence of vestigial tail-muscles. (The first drawing is copied from Prof. Watson's paper in _Journl. Anat. and Physiol._, vol. 79: the second is compiled from different specimens.)] (6) _Vermiform Appendix of the Cæcum._--This is of large size and functional use in the process of digestion among many herbivorous animals; while in man it is not only too small to serve any such purpose, but is even a source of danger to life--many persons dying every year from inflammation set up by the lodgement in this blind tube of fruit-stones, &c.