. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Skull of American Tritylodontidae • Sues 245. Figure 15. Articulated right quadrate and articular of Kayentatherium wellesi, MCZ 8811. A) medial view. B) lateral view. Based on camera lucida sketches. (, Fig. 16) with a forwardly directed "hook," which is closely similar to the manubrium mallei in monotremes (Hop- son, 1966: fig. 8; Kuhn, 1971: fig. 4). The hook has a relatively thick posterior rim, apparently corresponding to the orbicular apophysis on the monotreme malleus (Fleischer, 1973: fig. 1), a
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. Skull of American Tritylodontidae • Sues 245. Figure 15. Articulated right quadrate and articular of Kayentatherium wellesi, MCZ 8811. A) medial view. B) lateral view. Based on camera lucida sketches. (, Fig. 16) with a forwardly directed "hook," which is closely similar to the manubrium mallei in monotremes (Hop- son, 1966: fig. 8; Kuhn, 1971: fig. 4). The hook has a relatively thick posterior rim, apparently corresponding to the orbicular apophysis on the monotreme malleus (Fleischer, 1973: fig. 1), and is filled out by thin bone. The lateral surface faces an- terolaterally and is concave dorsoventral- ly. The distal extremity of the retroarticu- lar process is expanded and its ventral face is flat or gently concave. A foramen (), probably for the chorda tympani (VII), is developed on the medial aspect of the base of the retroarticular process just below the articular facet for the quad- rate trochlea. The chorda tympani would have had the same topographical position as in embryonic mammals (Fig. 23A). The articular facet () for the quad- rate trochlea forms a deeply concave notch, which is partitioned into a small lateral and a larger medial facet. It is overhung by a distinct dorsal lip except for its medial portion. The notch is delim- ited ventrally by a pronounced horizontal ridge (when viewed from behind). This ridge appears to be drawn out into an acute posterior projection () in lateral view, much as in Oligokyphiis (Kiihne, 1956: fig. 8). The articular notch is open medially. The medial facet is more con- cave than the lateral one. The transverse axis of the articular notch is strongly in- clined anteromedially (about 30° or 150°) relative to the long axis of the articular rod (MCZ 8811). A blunt projection locat- ed just anteroventral to the articular notch () is identical with a tubercle in Oli- gokyphiis (Kuhne, 1956: fig. 8B, "
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