50 



THE MERYCOIDODONTID/F. 



There is a small bone attached to the right stylohyal, which I interpret as the epihyal. If this 

 is correct, then the ceratohyal is missing in this specimen. This epihyal is a short, laterally com- 

 pressed bone, attached to the upper half of the distal end of the stylohyal and directed downward 

 at a greater angle than is the larger bone. 



The basihyal is a short transverse bar, vertically compressed. The superior surface is concave 

 and medially smooth, and at each end it has an elevated facet for articulation with the ceratohyal. 

 Inferiorly the surface is flattened and very slightly roughened. The posterior border is concave 

 and medially smooth, while from each side the posteriorly diverging thyrohyals branch off. The 

 anterior border carries the lingual process, which is roughly diamond-shaped in cross section. The 



/2239. YPM. 



Fig. 23. — Merycoidodon culbertsonii Leidy. Hyoid bones. Cat. No. 12239 Y.P.M. Nat. size. A. Stylohyal and 

 epihyal, side view. B. Thyrohyal, side view. C. Lingual process, basihyal, and thyrohyals, superior view. (After Thorpe, 

 1923.) 



inferior and superior surfaces are convex, but the latter is medially divided by a sharp ridge. The 

 lingual process is short, ending anteriorly in a rather blunt point. The basihyal, the lingual process, 

 and the thyrohyals are ankylosed, forming a unit that is shaped like a short-handled, two-tined fork. 



The thyrohyals extend backward, outward, and upward from the ends of the basihyal. They 

 are laterally compressed, gradually becoming more robust near the junction with the basihyal and 

 tapering toward the free (posterior) terminals. The anterosuperior end is somewhat excavated, 

 just posterior to its junction with the basihyal, except on the external side, which rises as a very 

 thin wall of bone for muscular attachment. 



The measurements in millimeters of these bones are briefly as follows: length of stylohyal 41 ; 

 maximum width of upper part of stylohyal (partly estimated) 8; length of epihyal 7.5; length of 

 basihyal 15; length of lingual process of the latter bone 6; and length of thyrohyal (partly 

 estimated) 26. 



The hyoid apparatus of Merycoidodon resembles that of Bos more than that of other Mam- 

 malia, exclusive of the Artiodactyla as a group. The major distinctions from Bos are: (1) the 

 muscular angle of the stylohyal in Merycoidodon is smaller, more like that in Equus; (2) the 

 lingual process is slenderer, more pointed, and relatively a little longer; (3) the thyrohyal is rela- 

 tively more robust. 



Therefore, if we may reason from analogy, it would seem that the tongue of Merycoidodon 

 was slightly less protrusible than that of Bos, much more so than that of any of the Perissodactyla, 

 but much less so than that of any of the Carnivora. 



