100 ' THE MERYCOIDODONTID/E 



becoming more robust near the junction with the basihyal and tapering toward the free posterior 

 ends. The anterosuperior end is somewhat excavated just posterior to the junction with the basi- 

 hyal, except for the outer side, which rises as a very thin wall of bone for muscular attachment. 

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



By rare good fortune the ossified thyroid cartilage of the larynx was found with, and just 

 posterior to, the hyoid apparatus in M. chelonyx. It is a hollow, compressed semicylinder, or 

 spout-shaped piece of bone, with exceedingly thin walls. The skull, with which this peculiar struc- 

 ture was associated, is very probably that of a male, and the structure may be a sexual distinction. 

 Scott likened this bone to that of the enormously inflated basihyal of the howling monkeys, and he 

 said that it must have given to these animals most unusual powers of voice. 



Skeleton: The atlas differs from that of Eporeodon in the more uniform width of the trans- 

 verse processes and their continuation into short spines behind the surfaces for the axis, and they 

 are more widely expanded laterally. There is no opening for the vertebrarterial foramen. The 

 neural spine is also larger and more rugose. The axis differs from Eporeodon chiefly in the more 

 spout-like odontoid process, the longer and heavier transverse processes, the hatchet-like neural 

 spine, and the more horizontal position of the postzygapophyses. The remaining cervicals are more 

 heavily built, but the neck is proportionally of about the same length as that of Eporeodon. The 

 dorsal vertebra are similar to those of the earlier genus but have better developed spines. 



The ribs are short, broad, and anteriorly compressed, becoming longer, much slenderer, and 

 more rounded posteriorly. 



By another fortunate circumstance Scott found with the skeleton of this species a rudimentary 

 clavicle. It lay in the matrix near the coracoid process of the scapula, extending forward and 

 inward and overlapping the first rib and the transverse process of the seventh cervical. In shape it 

 is very slender, rounded, and downwardly arched, with an inferior keel that is most prominent 

 medially and disappears toward the ends. Scott regards its presence as a persistent rudiment and 

 argues that that may explain why the acromion process is so large and prominent in the artiodactyles, 

 while even in the Eocene perissodactyles it is absent. 



The spine of the scapula is high and nearly median in position and has a distinct metacromial 

 process — a character unusual in this family. The acromion projects forward and downward. The 

 glenoid cavity is nearly round to slightly oval in outline, and the neck is moderately broad and 

 heavy. 



The humerus resembles that of Eporeodon, except that the shaft is stouter, the head is more 

 convex, and the external and internal tuberosities are less produced. The radius and ulna are 

 massive, unreduced, and not united. 



In the carpus the scaphoid has increased its size over that bone in Eporeodon. Scott (1895, 

 pp. 139-140) described the carpals as follows: 



The ulnar side of the scaphoid is concave and is chiefly occupied by the large inferior facet for the lunar. 

 The distal side is taken up by two facets, those for the magnum and trapezoid respectively. The magnum facet 

 is the larger of the two and is deeply excavated behind, but descends abruptly in front. The lunar is both high 

 and broad ; its radial surface is saddle-shaped concave from side to side and convex fore and aft, broad in front, 

 much contracted and tapering behind. The radial side carries two facets for the scaphoid, the upper one small 

 and nearly plane, the lower very large and convex and separated from the magnum surface by a scarcely per- 

 ceptible ridge. The latter facet is almost entirely lateral, except on the palmar border, where it is reflected under- 

 neath so as to be partly distal. The unciform facet is concave and obliquely placed; it forms with the magnum 

 surface a sharp beak, which is wedged in between the magnum and the unciform and extends nearly to the third 

 metacarpal. 



The cuneiform is broad and low and has a less dorso-palmar diameter than the other proximal carpals. The 

 ulnar surface is a narrow groove which is reflected down upon the external side of the bone, and the pisiform facet 

 forms a broad band upon the palmar side which is continuous with the ulnar facet. Distally, the cuneiform dis- 

 plays a simply concave facet for the unciform. The pisiform is intermediate in character between the condition 

 found in the earlier and that in the later genera of the family, being more expanded at the free end than in the 



