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Show 26 THE DESCENT OF MAN. PART. I. the soles of the feet are quite naked, like the inferior surfaces of all four extremities in most of the lower animals. As this can hardly be an accidental coincidence, we must consider the woolly covering of the fretus to be the rudimental representative of the first permanent coat of hair in those mammals which are born hairy. This representation is much more complete, in accordance with the usual law of embryological development, than that afforded by the straggling hairs on the body of the adult. It appears as if the posterior molar or wisdom-teeth were tending to become rudimentary in the more civilised races of man. These teeth are rather smaller than the other molars, as is likewise the case with the corresponding teeth in the chimpanzee and orang; and they have only two separate fangs. They do not cut through the gums till about the seventeenth year, and I am assured by dentists that they are much more liable to decay, and are earlier lost, than the other teeth. It is also remarkable that they are much more liable to vary both in structure and in the period of their development than the other teeth.31 In the Melanian races, on the other hand, the wisdom-teeth are usually furnished with three separate fangs, and are generally sound: they also differ from the other molars in size less than in the Caucasian races.32 Prof. Schaaffhausen accounts for this difference between the races by "the posterior dental portion of the jaw. being "always shortened" in those that are civilised,33 and this shortening may, I presume, be safely attributed to civi- 31 Dr. Webb,' Teeth in Man and the Anthropoid Apes,' as quoted by Dr. C. Carter Blake in' Anthropological Review,' July, 1867, p. 299. 32 Owen, • Anatomy of Vertebrates,' vol. iii. pp. 320, 321, and 325. 33 'On the Primitive Form of the Skull,' Eng. translat. in 'Anthropological Review.' Oct. 1868, p. 42G. CnAP. I. 1tUDIMENTS. 27 lised men habitually feeding on soft, cooked food, and thus usino- their jaws less. I am informed by Mr. Brace that it is becoming quite a common practice in the lJnited States to remove some of the molar teeth of children, as the jaw does not grow large enough for the perfect development of the normal number. With respect to the alimentary canal I have met with an account of only a single rudiment, namely the vermiform appendage of the ccecum. The ccecum is a branch or diverticulum of the intestine, ending in a cul-de-sac, and it is extremely long in many of the lower vegetable-feeding mammals. In the marsupial kaola it is actually more than thrice as long as the whole body.34 It is sometimes produced into a .long gradually-tapering point, and is sometimes constncted in parts. It appears as if, in consequence of changed diet or habits, the ccecum had become much shortened in various animals, the vermiform appendage being left as a rudiment of the shortened part. That this appendao- e is a rudiment, we may infer from its small size, a~d from the evidence which Prof. Oanestrini 35 has collected of its variability in man. It is occasionally quite absent, or again is largely developed. The passage is sometimes completely closed for half or two-thirds of its length, with the terminal part consisting of a flattened solid expansion. In the orang this appendage is long and convoluted: in man it arises from the end of the short ccecum, and is commonly from four to five inches in length, being only about the third of an inch in diameter. Not only is it useless, but it is sometimes the cause of death, of which fact I have lately heard two instances: this is due to small hard bodies, H Owen, • Anatomy of Vertebrates,' vol. iii. pp. 416, 434, 441. as 'Annuario della Soc. d. Nat.' Modena, 1867, p. 94. |