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Descent of Man [ 1871]

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Bullseye
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« on: February 09, 2009, 02:37:57 am »

* Eschricht, ibid., ss. 40, 47.
  *(2) See my Variation of Animals and Plants under Domestication,
vol. ii., p. 327. Prof. Alex. Brandt has recently sent me an
additional case of a father and son, born in Russia, with these
peculiarities. I have received drawings of both from Paris.

  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 have been assured that they are much more
liable to decay, and are earlier lost than the other teeth; but this
is denied by some eminent dentists. They are also much more liable
to vary, both in structure and in the period of their development,
than the other teeth.* 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.*(2) 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,*(3)
and this shortening may, I presume, be attributed to civilised men
habitually feeding on soft, cooked food, and thus using their jaws
less. I am informed by Mr. Brace that it is becoming quite a common
practice in the United 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.*(4)

  * Dr. Webb, "Teeth in Man and the Anthropoid Apes," as quoted by Dr.
C. Carter Blake in Anthropological Review, July, 1867, p. 299.
  *(2) Owen, Anatomy of Vertebrates, vol. iii., pp. 320, 321, and 325.
  *(3) "On the Primitive Form of the Skull," Eng. translat., in
Anthropological Review, Oct., 1868, p. 426.
  *(4) Prof. Montegazza writes to me from Florence, that he has lately
been studying the last molar teeth in the different races of man,
and has come to the same conclusion as that given in my text, viz.,
that in the higher or civilised races they are on the road towards
atrophy or elimination.

  With respect to the alimentary canal, I have met with an account
of only a single rudiment, namely the vermiform appendage of the
caecum. The caecum is a branch or diverticulum of the intestine,
ending in a cul-de-sac, and is extremely long in many of the lower
vegetable-feeding mammals. In the marsupial koala it is actually
more than thrice as long as the whole body.* It is sometimes
produced into a long gradually-tapering point, and is sometimes
constricted in parts. It appears as if, in consequence of changed diet
or habits, the caecum had become much shortened in various animals,
the vermiform appendage being left as a rudiment of the shortened
part. That this appendage is a rudiment, we may infer from its small
size, and from the evidence which Prof. Canestrini*(2) 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 caecum, 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, such as seeds, entering
the passage, and causing inflammation.*(3)

  * Owen, Anatomy of Vertebrates, vol. iii., pp 416, 434, 441.
  *(2) Annuario della Soc. d. Nat. Modena, 1867, p. 94.
  *(3) M. C. Martins ("De l'Unite Organique," in Revue des Deux
Mondes, June 15, 1862, p. 16) and Haeckel (Generelle Morphologie, B.
ii., s. 278), have both remarked on the singular fact of this rudiment
sometimes causing death.

  In some of the lower Quadrumana, in the Lemuridae and Carnivora,
as well as in many marsupials, there is a passage near the lower end
of the humerus, called the supra-condyloid foramen, through which
the great nerve of the fore limb and often the great artery pass.
Now in the humerus of man, there is generally a trace of this passage,
which is sometimes fairly well developed, being formed by a
depending hook-like process of bone, completed by a band of
ligament. Dr. Struthers,* who has closely attended to the subject, has
now shewn that this peculiarity is sometimes inherited, as it has
occurred in a father, and in no less than four out of his seven
children. When present, the great nerve invariably passes through
it; and this clearly indicates that it is the homologue and rudiment
of the supra-condyloid foramen of the lower animals. Prof. Turner
estimates, as he informs me, that it occurs in about one per cent of
recent skeletons. But if the occasional development of this
structure in man is, as seems probable, due to reversion, it is a
return to a very ancient state of things, because in the higher
Quadrumana it is absent.

  * With respect to inheritance, see Dr. Struthers in the Lancet, Feb.
15, 1873, and another important paper, ibid., Jan. 24, 1863, p. 83.
Dr. Knox, as I am informed, was the first anatomist who drew attention
to this peculiar structure in man; see his Great Artists and
Anatomists, p. 63. See also an important memoir on this process by Dr.
Gruber, in the Bulletin de l'Acad. Imp. de St. Petersbourg, tom. xii.,
1867, p. 448.

  There is another foramen or perforation in the humerus, occasionally
present in man, which may be called the inter-condyloid. This
occurs, but not constantly, in various anthropoid and other apes,* and
likewise in many of the lower animals. It is remarkable that this
perforation seems to have been present in man much more frequently
during ancient times than recently. Mr. Busk*(2) has collected the
following evidence on this head: Prof. Broca "noticed the
perforation in four and a half per cent of the arm-bones collected
in the 'Cimetiere, du Sud,' at Paris; and in the Grotto of Orrony, the
contents of which are referred to the Bronze period, as many as
eight humeri out of thirty-two were perforated; but this extraordinary
proportion, he thinks, might be due to the cavern having been a sort
of 'family vault.' Again, M. Dupont found thirty per cent of
perforated bones in the caves of the Valley of the Lesse, belonging to
the Reindeer period; whilst M. Leguay, in a sort of dolmen at
Argenteuil, observed twenty-five per cent to be perforated; and M.
Pruner-Bey found twenty-six per cent in the same condition in bones
from Vaureal. Nor should it be left unnoticed that M. Pruner-Bey
states that this condition is common in Guanche skeletons." It is an
interesting fact that ancient races, in this and several other
cases, more frequently present structures which resemble those of
the lower animals than do the modern. One chief cause seems to be that
the ancient races stand somewhat nearer in the long line of descent to
their remote animal-like progenitors.

  * Mr. St. George Mivart, Transactions Phil. Soc., 1867, p. 310.
  *(2) "On the Caves of Gibraltar," Transactions of the
International Congress of Prehistoric Archaeology, Third Session,
1869, p. 159. Prof. Wyman has lately shewn (Fourth Annual Report,
Peabody Museum, 1871, p. 20), that this perforation is present in
thirty-one per cent of some human remains from ancient mounds in the
Western United States, and in Florida. It frequently occurs in the
negro.

  In man, the os coccyx, together with certain other vertebrae
hereafter to be described, though functionless as a tail, plainly
represent this part in other vertebrate animals. At an early embryonic
period it is free, and projects beyond the lower extremities; as may
be seen in the drawing (see fig. 1) of a human embryo. Even after
birth it has been known, in certain rare and anomalous cases,* to form
a small external rudiment of a tail. The os coccyx is short, usually
including only four vertebrae, all anchylosed together: and these
are in a rudimentary condition, for they consist, with the exception
of the basal one, of the centrum alone.*(2) They are furnished with
some small muscles; one of which, as I am informed by Prof. Turner,
has been expressly described by Theile as a rudimentary repetition
of the extensor of the tail, a muscle which is so largely developed in
many mammals.

  * Quatrefages has lately collected the evidence on this subject.
Revue des Cours Scientifiques, 1867-1868, p. 625. In 1840
Fleischmann exhibited a human foetus bearing a free tail, which, as is
not always the case, included vertebral bodies; and this tail was
critically examined by the many anatomists present at the meeting of
naturalists at Erlangen (see Marshall in Niederland. Archiv fur
Zoologie, December, 1871).
  *(2) Owen, On the Nature of Limbs, 1849, p. 114.
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