134 DISCOVERY REPORTS 



of the maxilla, so that the anterior part of the upper jaw alters its position with reference 

 to the line of the cheek teeth and at the same time becomes more emphasized. The 

 temporal lines are closer together than they are in the fifth year, the sagittal suture has 

 become extremely complex and is beginning to show signs of fusion and supervening 

 obliteration from behind forward. 



In some of the summer skulls of this year the sagittal suture has disappeared and the 

 mastoid part of the periotic has begun to fuse with the cranium. 



Seventh year. There are only two skulls which can be placed in the winter group 

 of this year; the description, therefore, has been based on the slightly more advanced 

 skulls of the summer, although this increases the time interval between them and the 

 sixth year winter specimens. Eleven summer specimens, total length 2557 mm., 

 14-2 per cent of the body length; zygomatic width 140-9 mm., hamulo-premaxillar 

 length 1747 mm., 55-1 and 68-2 per cent of the skull length. These skulls are definitely 

 more massive and the ridges which mark the origin of the jaw muscles begin to be 

 conspicuous. The sagittal suture is entirely or almost entirely fused, and the coronal 

 suture begins to disappear from the middle line outwards. The sutures between the 

 mastoid part of the periotic and the cranium are usually partly obliterated. The palate 

 is usually more deeply excavated at the level of the zygomatic processes of the maxillae 

 than it is in the sixth year. 



Eighth year. Six specimens, total length 2617 mm., 14-2 per cent of the body 

 length; zygomatic width 145-3 mm., hamulo-premaxillar length 178-6 mm., 55-1 and 

 68-3 per cent of the skull length. Apart from increase in size and massiveness the prin- 

 cipal differences between this group and that which precedes it are to be found in the 

 more advanced state of sutural fusion. Besides further progress in the fusion of the 

 sutures mentioned under the seventh year, the palato-pterygoidal sutures begin to dis- 

 appear and sometimes the squamosal as well. All summer specimens. 



Ninth year. There are four skulls, all collected in summer and of large size which, 

 not having yet reached the condition of the final group, show nevertheless an advance 

 on the state of the eighth year. These must be regarded as forming a ninth year group 

 in which a further advance in average size is accompanied by still more complete fusion 

 of the bones of the skull. Four specimens, total length 261-9 mm., 14-0 per cent of the 

 body length; zygomatic width 145-8 mm., hamulo-premaxillary length i8i-8mm., 

 55-7 and 69-0 per cent of the skull length. 



The coronal sutures as well as the sagittal are usually obliterated. The squamosal 

 is fused to the parietal and to the alisphenoid and the latter to the frontal. The orbito- 

 sphenoid and the alisphenoid are also united and the pterygoids and palatines are fused. 



Tenth year and over. Eighteen specimens, total length 266-7 mm., 14-3 per cent 

 of the body length ; zygomatic width 151-7 mm., hamulo-premaxillar length 182-9 mm., 

 56-9 and 68-9 per cent of the skull length. This final group includes 18 which have all 

 well-fused sutures and with one exception, no. 502, well-developed muscular crests. 

 The projection of the pterygoids below the level of the alveolar ridges is conspicuous ; 



