350 .-i.Y.v.i/>.s' v/;ir yoKK ACAUiJAiv OF sr/i:.\cES 



I ndHsidiV . Tlic I iiiliisi<la' iiicludc ccilaiii lii<:iily specialized lemurs 

 from MadagasciU', such as tlu' Sifakas and Imliis. As compared with 

 the lower lemurs <iivat advances liave been made in tlic structure of the 

 teeth and in the size of the bi'ain-casc, i)ut the foiination id' the auditoi'y 

 bulla remains the same and tliis is one id' ilic ( liaiacters wliicli reveals 

 relationship with the typical lemurs. 



The Nycticebida^ include certain curiolisly modified lemuroids of 

 Africa and the oriental region, such as the slow loris and the galagos. 

 These lemuroids have uudergone considerable modification in the basi- 

 cranial region. It is much wider, the mastoid region in the back of the 

 skull is swollen up, the tympanic annulus is no longer concealed l)y the 

 bulla but lies as a short rim at the external border of the bulla. 



The South American monkeys of the family Cebidie differ markedly 

 from the lemurs as follows: the tympanic annulus is not concealed by 

 the auditory bulla but lies external to it and is closely joined with it. the 

 suture disappearing in the young animals. The base of the brain-case 

 has been greatly widened and the bulla itself is further in toward the 

 mid-line than it was in the lemurs. The tympanic thus forms a short 

 napkin-ring-like spout, called the bony auditory meatus. 



The monkeys of the Old World or catarrhine Primates. In these the 

 auditory bulla is not so much expanded as in preceding families. It is 

 pierced by a large canal or foramen for the carotid artery. The tym- 

 panic bone now form$ a greatly elongated spout leading to the outci- car. 

 In this slide we see the wide range in structure among the existing 

 macaques and baboons. Beginning with a short-faced more round-headed 

 m;u'aque we pass by almost imperceptible gradations to these very highly 

 specialized baboons with enormous elongated faces and massive jaws and 

 teeth. Amid all this diversity in form the structure in the auditory 

 region remains constant, as we see by comparing the most specialized 

 form, the mandrill, with the prim^itive form figured at' the left. 



We pass now to a much higher group of the Old World apes, the Sem- 

 nopithecina;, which includes the langurs, the guerezas, the long-nosed 

 monkey and others. Were it not for their high vegetarian specializa- 

 tions these monkeys, so far as the skull is concerned, might almost be 

 regarded as ancestral to man. Again we have a wide variation in form 

 fi-om short-faced to long-faced types, but the formation and arrangement 

 in the auditory region is the same as in all other Old World apes, namely, 

 the bulla is not greatly inflated and is pierced by the carotid foramen 

 or canal while the tympanic forms a long tapering spout. 



The antliropoid apes all agree again in the structure of the auditory 

 region. Here is the auditory bulla, pierced by the carotid canal, and 



