Page:Popular Science Monthly Volume 32.djvu/510

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O those who have already been startled by the memoir of Dr. W. Baldwin Spencer on the presence and structure of the pineal gland in Lacertilia, and the evidence that it represents a third eye in a rudimentary condition, it will be interesting to know that among some of the earlier mammals the pineal gland may have assumed functional importance as an eye. Professor Henry F. Osborn shows that in the skull of the curious mammal Tritylodon, of Owen, there is seen a parietal foramen in exactly the same position and relation as in the lizard Sphenodon.

Professor Osborn regards this fact of remarkable interest, as it adds greatly to the rapidly accumulating evidence for the reptilian affinities of the mammalia. Professor Owen, in the description of this unaccountable opening, suggested that it might be due to posthumous injury.

Professor Marsh, in a description of the skull of Diplodocus, a Dinosaur, describes a fontanelle in the parietal on the median line directly over the cerebral cavity. He adds, however, that this may be merely an individual variation.

Professor Cope observes an enormous fronto-parietal foramen in the skull of Empedocles molaris, a curious creature from the Permian.

It would appear evident from these facts that at one time the pineal gland, which in the mammals is in a rudimentary condition, and in certain Lacertilia sufficiently perfect, as an eye, to be sensitive to light impressions at least, was, in certain extinct mammals and reptiles, of large size and functionally active. It is a significant fact that no sooner does some one opposed to evolution undertake to lay down the law by setting a boundary to type-features, than a discovery is made that breaks down the barrier. Thus, Dr. Thomas Dwight, in an interesting memoir on the "Significance of Bone Structure," in which he makes a brave defense for teleology, says, in speaking of the persistence of the vertebrate plan, "There are never, for instance, more than two eyes or one mouth or two pairs of limbs," and, lo! an extra eye is immediately added.