x.] PRIMATES. 163 



the Cebida, in which animals the union of the parietal and 

 the alisphenoid separates the frontal from the squamosal, as 

 is usually the case with Man. The glenoid surface is 

 flatter than in Man, and there is a well-marked postglenoid 

 process. 



In the PlatyrrhincK) with the individual exception of 

 certain Afycetcs and Aides, the parietal and malar bones are 

 in contact with each other, separating the frontal from the 

 alisphenoid on the side wall of the skull. In the Catar- 

 r/rituc the reverse takes place, the alisphenoid and frontal 

 bones meeting each other and separating the malar from 

 the parietal. Another point of difference between the Old 

 and New World Monkeys is that in the latter is a small 

 slit in the malar wing not far from the point where the 

 malar, parietal and alisphenoid bones meet. This slit, 

 together with the infraorbito-temporal foramen, is the last 

 remnant of a wide orbito-temporal foramen. 



The zygoma is usually narrow, horizontal, and slightly 

 arched outwards. 



The periotic generally resembles that of Man, and the 

 mastoid portion is conspicious on the outer side of the 

 skull between the squamosal and the exoccipital ; but its 

 surface is smooth and rounded, without any distinct mas- 

 toid process. 



In all the Old World species, the tympanic forms an elon- 

 gated inferior wall to the external auditory meatus, which 

 has consequently a considerable bony tube ; but in all the 

 American Monkeys this bone retains more or less its primi- 

 tive annular condition, and the cavity of the tympanum is 

 close to the external wall of the cranium. This character 

 alone will readily serve to determine to which of the two 

 great divisions of Monkeys a skull may belong. 



No auditory bulla is developed in any of the Old World 



M 2 



