THE CYNOMORPHA. 397 



The brain varies remarkably in different Platyryhhii. In 

 Ohrysothrlx^ the cerebral hemispheres project beyond the 

 cerebellum to a Q-reater relative extent than in any other Mam- 

 mal, namely, by one-fifth of their total length. On the other 

 hand, in Mycetes^ the cerebral hemispheres hardly hide the 

 cerebellum, when the brain is viewed from above. 



In Cebus^ the outer surface of the brain is almost as much 

 convoluted as in the Catarrhine Apes. Ateles has the external 

 perpendicular fissure almost obliterated by the annectent gyri, 

 and, so far, exhibits a higher tjY^Q of brain than the Catar- 

 rhlni / but, in JPlthecia^ Ghrysothrix^ and Nyctlplthecus^ the 

 external sulci gradually disappear, until the brain is almost as 

 smooth as in the Marmosets. On the inner faces of the hemi- 

 spheres, however, the internal perjDcndicular, the calloso-mar- 

 ginal, the calcarine, and the collateral sulci remain, while, in 

 the interior of the hemispheres, the posterior cornu and the 

 hippocampus ininor are always present. 



The vermis of the cerebellum is large and projects beyond 

 the level of the posterior margins of its hemispheres ; the j^oc- 

 culus is large and lodged in a fossa of the 23eriotic ossification, 

 as in the Marmosets. The upper ends of the p^Tamids are 

 separated by corpora trapezoidea from \hQ pons Varolii. 



The penis is usually terminated by a large, button-sliaped 

 glans. The cavity of the tunica vaginalis is not shut oif from 

 the abdomen, and tlie testes lie at the sides of, rather than be- 

 hind, the penis. The female Ateles has a long clitoris, which 

 depends from the vagina. 



The JPlatyrrhini occur only in the Austro-Columbian prov- 

 ince, and are known in the fossil state only in certain caves 

 of that region. 



3. The GatarrJiini. — The Simiadm of this division present 

 a great range of variation in most respects, but they agree in 

 having the partition between the nostrils narrower than in the 

 JPlatyrrhini y in possessing a bony meatus auditorius ; in the 



dental formula ^. ^^^ ^* r^J P^^- ri ^^* Vi ^^^ ^^ being in- 

 habitants of the Old World. They fall into two very distinct 

 groups, the Gynomorpha and the Anthropomorpha. 



a. The Gynomorpha are distinguished from the other 

 group by being essentially quadrupedal, and usually provided 

 with a tail, which is never prehensile. The femur and tibia, 

 taken together, are longer than the humerus and the radius. 

 The outer inferior incisors are not larger than the inner ones, 

 but are often smaller. The crowns of the molar teeth present 



