. Anatomischer Anzeiger. Anatomy, Comparative; Anatomy, Comparative. 404 laginous foundation of the primitive ring and tympanum) is the modi- fied quadrato-jugal. This is not absolutely impossible, but it is un- necessary and very unlikely. The quadrato-jugal is often lost in closely allied Reptiles, for instance in various genera of Chelonia (in which, by the way, the whole quadrate is shaped into a huge tym- panic ring); it is also absent in various Theromorpha. Moreover, whenever it is still typically developed, e. g. in Lacertilia, it is mark- edly three-armed, rather like the os tympanicu
. Anatomischer Anzeiger. Anatomy, Comparative; Anatomy, Comparative. 404 laginous foundation of the primitive ring and tympanum) is the modi- fied quadrato-jugal. This is not absolutely impossible, but it is un- necessary and very unlikely. The quadrato-jugal is often lost in closely allied Reptiles, for instance in various genera of Chelonia (in which, by the way, the whole quadrate is shaped into a huge tym- panic ring); it is also absent in various Theromorpha. Moreover, whenever it is still typically developed, e. g. in Lacertilia, it is mark- edly three-armed, rather like the os tympanicum of low Mammals, with a shaft eventually attached to the squamosal and to the mandible, and with a third, free arm, but this free arm of the quadrato-jugal points forwards, not backwards; the articulation of the quadrato-jugal with the mandible is effected by the most lateral, external portion of the articulare, or even with the lateral splint bone, the supra-angulare. The primitive os tympanicum on the other hand is articulated with the innermost part of the articulare. Of course those, who favour the quadrate = incus view, fight shy of a survey of the features of the OS tympanicum. Macroscopic dissection, the observation of actual facts, leave alone the examination of a large series of different genera, are discarded for ontogenetic, mostly cenogenetic vagaries. Peters had interpreted the distal knob of the shaft of the tympanic of Echidna as the old articulation with the mandible and I have further elaborated his sagacious observation by suggesting that this knob of the tympanic originally articulated with that part of the mandible, which in Mar- supials is known as its inner angle. This I am now able to prove. Mr. Oldfield Thomas has kindly permitted me to examine two very young specimens of Orycteropus, probably foetuses, and a very immature skull. Another skull has been figured in Phil. Trans, op. cit. PI. 73, Fig. 28. In the two youngest of these skulls the conditions a
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