210 MEMOIES OF THE NATIONAL ACADEMY OF SCIENCES. 



shown beyond question that one or both of these horns may be wanting. One was wanting in a girl of 17 and both 

 in a man of 55. In a woman, said to be 80, one was wanting and the other probably wanting. In a man of 37 and 

 another of 39 one was probably wanting. In a woman 50 and a man 55 both were probably wanting. When a joint 

 was found upon the body it was clear that the lesser horns had been lost, which occurred two or three times; but 

 the absence of a joint does not show beyond question that the horn was wanting as it may have been held by ligament. 

 It is thought most probable that where the entry has been made &quot;lost or wanting,&quot; the bone was originally wiiuting. 



We come now to consider tlie body of the hyoid boue, and we regret to say that the soft parts 

 particularly the larynx, could not be included in this study since our material refers almost exclu 

 sively to the dry bone itself. The body of the hyoid in monkeyshas a distinctive and characteristic 

 form, which according to Flower* has a greater vertical than transverse diameter (see figs. 40 and 

 41). This form of the hyoid body is associated in many of the lower types of monkeys with a 

 membranous sack which occupies the concavity of the bone and protrudes between the lower edge 

 of the body and the upper edge of the thyroid cartilage. It was called the hyothyroideau sac by 

 Cuvier, and the succus mcmbranaceus by Wolf. It has an opening at the base of the epiglottis 

 and is said to sometimes communicate with the laryngeal sac which lies just above the vocal chords. 

 According to Eckhard,t this hyothyroidean sac is absent in the anthropoid apes, with the possible 

 exception of the gibbon. We are not sufficiently familiar with the anatomy of the larynx of the 

 anthropoids to state whether any rudiment of this condition is to be found in them; but it would 

 not be at all surprising if this eventually turns out to be the case. We are led to infer that the 

 true significance of the great depth of the body of the hyoid in the monkey is to be explained 

 primarily upon the basis of this sac, whatever its function may be, and that the depth of the body 

 in proportion to its width furnishes an index of this distinctively simian feature, which we propose 

 to call the basihyal index. 



A/I, 



Flo. 40. Hyoid of baboon; bh, basibyal; th, thy- FIG. 41. Hyoid of an American monkey; th, thyrohyal; 



rohyal. [After Flower.] ch, ceratohyal; eh, epihyal. [After Flower.] 



It is therefore with no small amount of interest that we come to examine this question in the 

 light of our present material. We have been necessarily compelled to limit our researches to the 

 Negro and Saladoan, for the reason that our materials have proven insufficient as regards other 

 races, which are therefore not included. Some difficulty has been experienced in determining just 

 where the measurements should be taken in case the greater cornua are coossificd with the body, 

 which is, as we have seen, the usual condition of the adult Negro hyoid. After careful attention 

 to this point we have determined upon the following measurements : The vertical depth is obtained 

 by placing the bone flatwise upon its posterior surface and measuring with a pair of calipers or 

 other suitable instrument its greatest diameter in this direction. The transverse diameter is taken 

 by placing one arm of the dividers upon the point of union of the anterior ridge with the lingual 

 or superior border and measuring to the corresponding point upon the opposite side. In some 

 instances the anterior transverse ridge is not well defined and the point where it terminates is not 

 easily made out. In such cases, if there- remain any traces of the suture joining the great cornua 

 with the body we measure from this suture where it crosses the superior border to the same point 

 upon the opposite side. 



Among the Saladoans the bodies are mostly free and we have had little difficulty in determin 

 ing the proportion of the depth to the width. In one instance we measured the greatest diameters 

 and found that the proportion of the depth to the width is 52 per cent and a fraction in 45 speci 

 mens. In the same series measured between the points indicated above for the transverse diameter 

 the proportion is 54 per cent. 



* FLOWER: Osteology of the Mammalia, p. 140. 



t MULLEH: Archiv fiir Auatomie and Physiologie, 1847, p. 44. 



