468 THE ANATOMY OF VEETEBEATED ANIMALS. 



The brain varies remarkably in different Platyrrhini. In 

 Chrysothrix, the cerebral hemispheres project beyond the 

 cerebellum to a greater relative extent than in any other 

 Mammal, namely, by one-fifth of their total length. On 

 the other hand, in Mycetes, the cerebral hemispheres 

 hardly hide the cerebellvim, when the brain is viewed from 

 above. 



In Cebus, the outer surface of the brain is almost as 

 much convoluted as in the CataiThine Apes. Ateles has the 

 external perpendicular fissure almost obliterated by the 

 annectent gyi'i, and, so far, exhibits a higher type of brain 

 than the Catarrhini; but, in Pitheda, Chrysothrix and 

 Nydipithecus, the external sulci gradually disappear, until 

 the brain is almost as smooth as in the Marmosets. On 

 the inner faces of the hemispheres, however, the internal 

 pei-pendicular, the calloso-marginal, the calcai-ine, and 

 the collateral sulci remain, while, in the interior of the 

 hemispheres, the posterior cornu and the hippocampus minor 

 are always present. 



The vermis of the cerebellum is large and projects beyond 

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

 cuhcs is large and lodged iu a fossa of the periotic ossifica- 

 tion, as in the Marmosets. The upper ends of the pyi'amids 

 are separated by corpora trapezoidea from the pons Varolii. 



The penis is usually terminated by a large button-shaped 

 glans. The cavity of the tunica vaginalis is not shut off 

 from the abdomen, and the testes lie at the sides of, rather 

 than behind, the penis. The female Ateles has a long 

 clitoris, which depends from the vagina. 



The Platyrrhini occui* only in the Austro-Columbian pro- 

 vince, and are known in the fossil state only in cez'tain 

 caves of that region. 



3. The Catarrhini. — The Simiadce 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 Platyrrhini ; in possessing a bony meatus auditorius ; 



2*2 1*1 2*2 3*3 



in the dental formula ^- .t:^ <'• jry P-''^- ^ ^'^* '^> ^^^ ^ 



