. Bulletin. Natural history; Natuurlijke historie. OSTEOLOGY OF DEINONYCHUS ANTIRRHOPUS 17 MAXILLA The right maxilla of YPM 5232 is nearly complete and only slightly crushed (Fig. 6). In lateral view, it is triangular in shape, with the narrow apex directed. FIG. 6. Snout of Deinonychus antirrhopus, skull YPM 5232, right side viewed in reverse. Notice the subsidiary antorbital fenestrae. Abbreviations: aof—antorbital fenestra; aof' and aof"—sub- sidiary antorbital fenestrae; en—external naris; ma—maxilla; na—nasal; pm—premaxilla. forward and the rear margin deeply emarginated by the anter
. Bulletin. Natural history; Natuurlijke historie. OSTEOLOGY OF DEINONYCHUS ANTIRRHOPUS 17 MAXILLA The right maxilla of YPM 5232 is nearly complete and only slightly crushed (Fig. 6). In lateral view, it is triangular in shape, with the narrow apex directed. FIG. 6. Snout of Deinonychus antirrhopus, skull YPM 5232, right side viewed in reverse. Notice the subsidiary antorbital fenestrae. Abbreviations: aof—antorbital fenestra; aof' and aof"—sub- sidiary antorbital fenestrae; en—external naris; ma—maxilla; na—nasal; pm—premaxilla. forward and the rear margin deeply emarginated by the anterior boundary of the large antorbital fenestra. The upper margin forms a nearly straight, forward- sloping contact with the nasal. The anterior margin curves downward to form a moderately broad, digitate suture with the premaxilla. The inferior margin is straight and not curved or undulating as in Allosaurus, Gorgosaurus and Tyran- nosaurus. Posteriorly, both upper and lower processes taper gradually to re- stricted contacts with the lachrymal and jugal respectively. The alveolar groove contains 7 functional teeth, 3 incompletely erupted re- placement teeth and 5 additional vacant alveoli, for a total of 15 maxillary teeth. This compares with 16 to 18 in Allosaurus, and 13 and 12 respectively in Gorgo- saurus and Tyrannosaurus. Coelophysis bears 16 to 22 maxillary teeth and Orni- tholestes^ has 9 or 10. The largest tooth is situated at about mid-length of the tooth row. The last 4 to 6 alveoli appear to have contained somewhat smaller teeth than those preserved along the remainder of the tooth row. The lateral surface above the alveolar mar- gin is marked by numerous foramina arranged in two more or less distinct rows 3 Examination of the type specimens has led me to conclude that Ornitholestes and Coelurus may not be synonymous. Until thorough comparisons can be made, I prefer to consider these as distinct and to use Ornitholestes in reference to the American Museum
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