matter. But the hall-mark of truth is not always simplicity; indeed the converse appears to be frequently the case. And on the whole this view does not commend itself to zoologists at present. For it must be borne in mind that the lower jaw of the mammal is not the precise equivalent of that of the reptiles. Apart from the membrane bones, which may be collectively the equivalents of the dentary of the mammal, there is the cartilaginous articular bone to be considered, which forms the connexion between the rest of the jaw and the quadrate in reptiles. Even in the Anomodontia, whose relations to the Mammalia are considered elsewhere, there is this bone. But in these reptiles the articular bone articulates not only with the quadrate, but also to a large extent with the squamosal, the quadrate shrinking in size and developing processes which give to it very much the look of either the incus or the malleus of the mammalian ear. In fact it seems on the whole to fit in with the views of the majority, as well as with a fair interpretation of the facts of embryology, to consider that the chain of ear bones in the mammal is not the equivalent of the columella of the reptile, but that the stapes of the mammal is the columella, and that the articulare is represented by the malleus and the quadrate by the incus. It is very interesting to note this entire change of function in the bones in question. Bones which in the reptile serve as a means of attachment of the lower jaw to the skull are used in the mammal to convey the waves of sound from the tympanum of the ear to the internal organ of hearing.
Another important and diagnostic feature in the mammalian skull is that the first vertebra of the vertebral column always articulates with two separate occipital condyles, which are borne by the exoccipital bones and formed mainly though not entirely by them. Certain Anomodontia form the nearest approach to the mammals in this particular. The two condyles of Amphibia are purely exoccipital in origin.
In the Mammalia, unlike what is found in lower Vertebrates (but here again the Anomodontia form at least a partial exception), the jugal arch does not connect the face with the quadrate, for, as already said, that bone does not exist, in the Sauropsidan form, in mammals. This arch passes from the squamosal to the maxillary, and has but one separate bone in addition to those two, viz. the jugal or malar.
