Peterson: The Osteology of Promerycochcerus. 



163 



the crowns of the teeth. The temporal fossa is rather shallow and 

 occupies a small area immediately below the sigmoid notch. Below 

 the temporal fossa the external face of the angle is gently convex 

 supero-inferiorly further back it is concave due to the heavy border 

 of the angle, while anteriorly the masseter muscle seems to have been 

 bounded by a prominent ridge, which extends almost vertically down- 

 ward opposite the last lobe of M^ (cf. PI. XXXVIII). When the 

 lower jaws are placed in position there is a very wide space between 

 the external face of the angle and the zygomatic arch, which indicates 

 that the masseter muscle was thick above. 



Fig. 3. Posterior view of the ossified thyroid cartilage of the larynx of Mycetes 

 seniculus, C. M. Cat. Mammals No. 3579, J natural size; i, posterior view; 2 and 

 3, side and posterior views, Promerycochcerus carrikeri. No. 1079. Ch. Articulations 

 for the ceratohyals. 



The Thyroid Cartilage of the Larynx. (Fig. 3). — In the description 

 of the hyoid apparatus of Mesoreodon Professor Scott describes and 

 figures what he regards as unmistakably the ossified thyroid cartilage 

 of the larynx (/. c, pp. 130-131, PL III, Fig. 9). Not far out of position 

 and still between the angles of the lower jaws of the middle skeleton 

 (No. 1079) of the group under discussion is found a similar spout- 

 shaped bone which is undoubtedly the ossified thyroid cartilage of the 

 larynx. As in Mesoreodon this bone is very thin on the sides and below. 

 Posteriorly its border is thickened, not to the same extent as in Mycetes 

 seniculus, but cjuite similarly. This bone is, however, not entirely 

 covered over so as to form a drum or capsule, nor has it the relatively 

 enormous size found in the howling monkey, but its shape suggests 

 the same function. 



