The significance of anomalies / by Thomas Dwight.

  • Dwight, Thomas, 1843-1911.
Date:
1895
Catalogue details

Licence: Public Domain Mark

Credit: The significance of anomalies / by Thomas Dwight. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    1895.] 133 The Significance of Anomalies. describes as pronator manus is Cryptobranchus Japonicus and of one described by Meckel in chelonians. It is curious that Macalister has found this arrangement in a tiger and I have found it in both arms of a chimpanzee, which I believe is an unique observation. This shows a tendency in the carnivora and primates to similar variation which is not inherited. Some of these anomalies present a likeness that is very probably accidental, possessing no significance whatever. Such is the peculiar union of the different pieces of the ster- num by which the manubrium fuses with what should be the first piece of the meso-sternum. Is the fact that this frequent- ly occurs in the gibbons to be looked upon as anything but a coincidence? Does the occasional perforation of the thyroid cartilage by the superior laryngeal nerve in man derive any significance from the fact that this is found in the seal? Again, when we find in man some anomaly of the aortic arch or of the great arteries springing from it, we know that the usual course of development of the branchial arches has been disturbed. Need we look further than to some accident in the individual ? Has the fact that the abnormal arrangement is nor- mal in some animal any significance? These are questions which admit of no certain answer. The second class of anomalies are those of most difficult explanation. They naturally suggest an analogy with the cases of the occurrence of similar structures in widely separ- ated animals, such as the bill of a duck and of the Ornitho- rhyncus, the paddle of the cetacean and of the ichthyosaurus. The obvious retort is that these resemblances are superficial ; but they are none the less true. Indeed, similar arrangements for a similar purpose are found which can in no way be called superficial. A very good example is furnished by Mr'. Dobson.4 The Pyrenean water mole (Myogale) of the Insectivora, which has very elongated digits, has an enormously devel- oped fibular flexor and a rudimentary tibial flexor. On the true moles the tibial flexor is larger, but the arrangement is 4On the Comparative Variability of Bones and Muscles, etc. Journal of Anat. and Phys. Vol. XIX. p. 20.