the SkuU of DiademoJon. ?^'l'^ 



4. It lias a posterior process passing backwards towards 

 the point of articulation of the lower jaw, which articulates 

 Mith a process of the periotic and forms the anterior wall ot 

 the tyn)|)anurn. 



5. Lastly, the caroticus intcrniis enters the cranial cavity 

 thron«:;h a canal l)ct\vceu the posterior ramus of the ptery- 

 goid and the ba>isplienoid. 



The alisphenoid of Daxyun/s has the following relations : — 



1. It articulates with the basispheno'd. 



"2. It has a large ascending process which articulates with 

 tlie parietal, separates the exits of the II., III., IV., V,^, 

 and \l. nerves from tliose of the second and third divisions 

 of the V. (which, however, pass through it and not behind it). 



3. It has an anterior ])art articulating with the palatine 

 and the " pterygoid, ^^ which lies on its inner or ventral 

 surface. Internally it is sej)arated from its fellow by the 

 vomer and the basisphcnoid. 



4. It has a posterior process running back towards the 

 point of articulation of the lower jaw, which articulates with 

 the periotic and forms the anterior wall of the tympanum. 



5. Lastly, the caroticus internus enters the brain-cavity 

 through a canal lying between the posterior process and the 

 basisphcnoid. 



Dasijurits is not exceptional in these relations, which are 

 found with only slight variations in all ]Marsupials, and from 

 which those of higher ]\Iamnials only differ in the reduction 

 of the posterior process of the alisphenoid, which is, however, 

 found in a reduced form in many Insectivores. 



The relations of the pterygoid of Cynodonts (which are 

 essentially similar to those of the pterygoids of other primi- 

 tive Reptiles) are so exactly similar to those of the alisphenoid 

 of primitive Mammals, as described above, that the con- 

 clusion that the alisphenoid of Mammals represents the 

 pterygoid of Cynodonts (and other Reptiles) is to me 

 irresistible. 



This conclusion is, I believe, new; but Parker and Cope 

 have held that the epipterygoid of Reptiles was the alisphenoid 

 of Mammals. 



So far as I know, the only evidence against the view tl.iat 

 I have just urged is that 'the pterygoid of Reptiles is a 

 membrane bone, whereas the mammalian alisphenoid is a 

 cartilage bone. This difficulty docs not seem to me a very 

 serious one : the tendency nowadays is to lay less and less 

 stress on this difierenee, and in any case the whole pterygoid 



