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rudiments, however, may occur in one sex
of those parts which are normally present in the other sex; and such
rudiments, as we shall hereafter see, have often originated in a way
distinct from those here referred to. in some cases, organs have been
reduced by means of natural selection, from having become injurious to the
species under changed habits of life. the process of reduction is probably
often aided through the two principles of compensation and economy of
growth; but the later stages of reduction, after disuse has done all that
can fairly be attributed to it, and when the saving to be effected by the
economy of growth would be very small (23. |
| some good criticisms on this
subject have been given by messrs.
the final and complete suppression of a part, already useless and much
reduced in size, in which case neither compensation nor economy can come
into play, is perhaps intelligible by the aid of the hypothesis of
pangenesis. |
but as the whole subject of rudimentary organs has been
discussed and illustrated in my former works (24.
rudiments of various muscles have been observed in many parts of the human
body (25. 13) describes and figures rudiments of
what he calls the "muscle pedieux de la main," which he says is sometimes
"infiniment petit." another muscle, called "le tibial posterieur," is
generally quite absent in the hand, but appears from time to time in a more
or less rudimentary condition.); and not a few muscles, which are regularly
present in some of the lower animals can occasionally be detected in man in
a greatly reduced condition. every one must have noticed the power which
many animals, especially horses, possess of moving or twitching their skin;
and this is effected by the panniculus carnosus. remnants of this muscle
in an efficient state are found in various parts of our bodies; for
instance, the muscle on the forehead, by which the eyebrows are raised. |
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the platysma myoides, which is well developed on the neck, belongs to this
system. turner, of edinburgh, has occasionally detected, as he
informs me, muscular fasciculi in five different situations, namely in the
axillae, near the scapulae, etc., all of which must be referred to the
system of the panniculus.) that the
musculus sternalis or sternalis brutorum, which is not an extension of the
rectus abdominalis, but is closely allied to the panniculus, occurred in
the proportion of about three per cent. in upwards of 600 bodies: he adds,
that this muscle affords "an excellent illustration of the statement that
occasional and rudimentary structures are especially liable to variation in
arrangement. |
| de candolle has communicated to me a curious instance of
the long-continued persistence or inheritance of this power, as well as of
its unusual development. he knows a family, in which one member, the
present head of the family, could, when a youth, pitch several heavy books
from his head by the movement of the scalp alone; and he won wagers by
performing this feat. his father, uncle, grandfather, and his three
children possess the same power to the same unusual degree. this family
became divided eight generations ago into two branches; so that the head of
the above-mentioned branch is cousin in the seventh degree to the head of
the other branch. this distant cousin resides in another part of france;
and on being asked whether he possessed the same faculty, immediately
exhibited his power. |
| this case offers a good illustration how persistent
may be the transmission of an absolutely useless faculty, probably derived
from our remote semi-human progenitors; since many monkeys have, and
frequently use the power, of largely moving their scalps up and down. i have seen one
man who could draw the whole ear forwards; other men can draw it upwards;
another who could draw it backwards (28.); and from what one of these persons told me, it is probable that
most of us, by often touching our ears, and thus directing our attention
towards them, could recover some power of movement by repeated trials. the
power of and directing the shell of ears to various points
of the compass, is doubt of highest service to animals, as they
thus perceive the direction of ; but have never heard, on
sufficient evidence, of man who possessed this power, the one which might
be of to . the whole external shell may be a ,
together with various folds and prominences (helix and anti-helix,
tragus and anti-tragus, etc. |
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