OCR Text |
Show 192 THE DESCENT OF MA:'f. ; PART L wards, and the lower eyelids wrinkled. The _external oars are curiously alike. In man the nose IS much more prominent than in most monk_eys; but we m~y trace the commencement of an aqmhno curvature m the nose of the Hoolock Gibbon ; and this in the Semnopithecus nasica is carried to a ridiculous extreme. . The faces of many monkeys are ornamented w1th beards whiskers, or moustaches. The hair on the head grows 'to a great length in some species of Semnopitbecus; 6 and in the Bonnet monkey (Ma~acus radiatus) it radiates from a point on the crown, with a parting down the middle, as in man.. It is com~only said that the forehead gives to man h1s noble and mtellectual appearance; but the thick hair on the head of the Bonnet monkey terminates abruptly downwaru~, and is succeeded by such short and fine hair, or down, that at a little distance the forehead, with the exception of tho eyebrows, appears quite naked. It has been erroneously asserted that eyebrows are not present in any monkey. In the species just named the deg1·ee of nakedness of the forehead differs in different individuals; and Eschricht states 7 that in our children the limit between the hairy scalp and the naked forehead is sometimes not well defined ; so that here we seem to have a trifling case of reversion to a progenitor, in whom the forehead had not as yet become quite naked. It is well known that the hair on our arms tends to converge from above and below to a point at the elbow. This curious arrangement, so unlike that in most of the lower mammals, is common to the gorilla, chimpanzee, orang, some species of Hylobates, and even to some few American monkeys. But in Hylobates agilis the hair 6 Isid. Geoffroy,' Hist. Nat. Gen.' tom. ii. 1859, p. 217. 1 ''Ueber die Richtung der Hmue," &c., 1\iiiller's 'Archiv fiir Anat. und Pbys.' 1837, s. 51. CHAP. VI. AFFINITIES AND GENEALOGY. 193 on the fore-arm is directed downwards or towards the wrist in the ordinary manner; and in H.lar it is nearly erect, with only a very slight forward inclination; so that in this latter species it is in a transitional state. It can hardly be doubted that with most mammals the thickness of the hair and its direction on the back is adapted to throw eff the rain; even the transverse hairs on the fore-legs of a dog may serve for this end when he is coiled up asleep. Mr. Wallace remarks that the convergence of the hair towards the elbow on the arms of the orang (whose habits he has so carefully studied) serves to throw off the rain, when, as is the custom of this animal, the arms are bent, with the hands clasped round a branch or over its own head. vVe should, however, bear in mind that the attitude of an animal may perhaps be in part determined by the direction of the hair ; and not the direction of the hair by the attitude. If the above explanation is correct in the case of the orang, the hair on our fore-arms offers a curious record of our former state; for no one supposes that it is now of any use in throwing off the rain, nor in our present erect condition is it properly directed for this purpose. It would, however, be rash to trust too much to the principle of adaptation in regard to the direction of the hair in man or his early progenitors; for it is impossible to study the figures given by Eschricht of the arrangement of the hair on the human footus (this being the same as in the adult) and not agree with this excellent observer that other and more complex causes have intervened. The points of convergence seem to stand in some relation to those points in the embryo which are last closed in during development. There appears, also, to exist some relation between the arrangement VOL. I. 0 |