532 



Dil. C. W. ANDREWS ON THE 



terminates in front in the post-orbital process [p.oi^b.). Towards its 

 anterior end it becomes very prominent, sharply delimiting the 

 ej^e-socket above. This ridge seems to be very characteristic of 

 the Proboscidea : it occurs in Mce.ritheriuvi and probably in all 

 the members of the group. 



The skull of Binotherium is. in many respects, one of the most 

 remarkable known. Although fundamentally its characteis are 

 clearly Proboscidean, nevertheless it differs widely from tlie skulls 

 of the other members of the group and, indeed, in some respects 

 from that of any other mammal. In the true Elephants and 



Text-figure 4. 

 n.f. 



a.s. 



Skull of Dinotherium giganteum. 

 From behind : about -^3 iiat. siee. 



a.s., OTitev angle of squamosal ; y.i»., foramen magnum; n.f., nuchal fossa; o.c, 

 occipital condyle; p.n., posterior nares; p.p., paroccipital process; pt.fl., 

 post-tympanic flange; r., ridge from outer angle of squamosal. 



Mastodons the peculiar form of the skull is mainly due to the 

 enormous development of cellular bone in the occipital region, 

 increasing the area available for the attachment of the muscles 

 necessary for the support of the heavy trunk and tusks. In 

 Dinothervmn, although the upper tusks are wanting, the trunk, 

 judging from the large size of the nasal opening, must have been 

 enormous, and the weight of the head was further increased by 

 the great deflected mandibular symphysis with its large tusks. 

 In thisca,se, however, the area for the attachment of the support- 

 ing muscles was supplied by the widening out of the occipital 

 surface, which was further increased laterally by the extension 

 outwards of the squamosals. Little or no cellular bone seems to 

 have been developed, the occipital surface above the post -tympanic 

 flanges being nearly {la,t except for the depression for the nuchal 



