0. G. May^s h — Origin of Mammals. 407 



The different kinds of teeth seen in the reptiles regarded as 

 mammalian in type, I consider of comparatively small import- 

 ance, for the reason that the same general forms of teeth are to 

 be found, not merely in the reptiles supposed to be nearest to 

 mammals, but also in other groups widely different. In the 

 Crocodiles, for example, the extinct genus Notosuchus, recently 

 discovered in Patagonia, has all three kinds of teeth well dis- 

 tinguished. Again, some of the Dinosaurs, especially the 

 genus Triceratojjs, have teeth with two roots, a supposed 

 mammalian character. In some Fishes, also, {Anarrhichas) 

 three kinds of teeth may be seen. It is more than probable, 

 therefore, that the peculiar resemblance between the teeth of 

 mammals and those of the lower vertebrates is merely one of 

 parallel development, the adaptation being along similar lines, 

 and in no sense an indication of genetic affinity. 



The great development of the squamosal bone in Theriodont 

 reptiles is not alone, for somewhat similar proportions are found 

 in some other reptiles, for example, in the Plesiosaurs, where 

 the squamosal is very large, and wrapped round the quadrate. 

 In some of the Dinosaurs, also, (Torosaurus) the squamosal has 

 an enormous development, while the quadrate remains of very 

 moderate size. 



The quadrate bone, always present in Birds, Reptiles, and the 

 other lower vertebrates, is well-known as the suspensorium of 

 the lower jaw, which meets it with a concave articular face. 

 The quadrate, however, appears to be wanting in mammals, or 

 at least has not yet been identified with certainty. 



What represents the quadrate bone in mammals, is a vexed 

 question in itself, and some of the best anatomists in the past, 

 Cuvier, Owen, Peters, Huxley, and others, have endeavored to 

 solve the problem. The tympanic bone, the incus, and the 

 malleus have each in turn been regarded as the remnant of the 

 quadrate, but up to the present time the question has not been 

 settled. It is not improbable that the quadrate may have 

 coalesced with the squamosal. 



The occipital condyles of mammals, as well known, are two 

 in number, and separated from each other. This is not the 

 case with any true reptile, although the contrary has been 

 asserted. The nearest approach appears to be where there is 

 a single bifid condyle, cordate in shape, with the two lobes 

 meeting below, as in some reptiles and a few birds, but not 

 separate as in mammals and amphibians. 



Finally, in all known mammals, recent and extinct, the 

 lower jaw is composed of a single piece, and has a convex con- 

 dyle meeting the skull by a distinct articulation. All reptiles, 

 even those supposed to be nearest the mammals, have the 

 lower jaw composed of several pieces, and these show distinct 

 sutures between them, a profound difference that must be 

 explained away before an approach can be made between the 

 two classes. 



