THE PLATTREHINI. 467 



cerebral cavity. The premaxillo-raaxillary suture disappears 

 early in Cebus. 



The formiUa of the adult dentition is i. ^ c. -^ p.vi. .-7- 



3*3 

 in. — = 36. The crowns of the molar teeth usually have 



two transverse ridges, ending in four cusps. In the upper 

 molars of Ateles and Mycetes an oblique ridge crosses the 

 crown from the antero-external to the postero-intemal 

 cusp. The pennanent canines usually make their appear- 

 ance before the last molar. 



The stomach is simple, the ccecum large, and devoid of 

 any venniform appendix; the liver is usually five lobed; 

 and the kidney has a single papilla. 



The ventricles of the larynx are not usually developed 

 into air-sacs. In Ateles, however, a median air-sac is deve- 

 loped from the posterior waU of the windpipe between the 

 cricoid cartilage and the first ring of the trachea. A very 

 remarkable modification of the hyoid and larynx takes 

 place in Mycetes. The cornua of the hyoid are rudi- 

 mentary, but its body is converted into a large thin-walled 

 bony di'um, the cavity of which communicates, beneath the 

 large epiglottis, with that of the lai-ynx. The thyi'oid 

 cartilage is very large, and the cartilages of Wrisberg and 

 Santorini are replaced by a fibrous mass, which is united 

 posteriorly with its fellow of the opposite side. In addition 

 to the hyoidean air-sac the ventricles of the larynx are 

 dilated and prolonged upwards, coming into contact above 

 the larynx ; two pharyngo-laryngeal pouches may be added 

 to these. Mycetes is famous for the distance to which its 

 howling voice can be heard in the South American forests. 



Although the pollex is i-udimentary and apparently func- 

 tionless in Ateles, all its chai'acteristic muscles {abductor, 

 adductor, flexor brevis, and opponens) are present, except the 

 long flexor. 



In Nyctipithecus the pedal interossei avejlexores breves, and 

 lie on the plantar surfaces of the metatarsal bones, as in 

 the Marmosets; but both the adductor hallucis and the 

 transversus pedis are well developed. 



