210 DEVELOPMENT OF THE MARSUPIAL SKULL, 



The large lateral cartilage which I have referred to as the 

 orbitosphenoid, Gaupp calls by various names. The anterior 

 part he calls the ala orhitalis. A little further back it is called 

 the commissura orhito-j)arietalis', while, when it passes above the 

 auditory capsule, it becomes the lamina supracapsularis. In 

 Echidna^ however, the cartilage is essentially similar to that in 

 the marsupials. 



The monotreme auditory " ossicles " chiefly differ in the small 

 size of the incus. 



Comparison of the Marsupial Primordial Skull with that of the 



Eutheria. 



Much more work requires to be done before anything like a 

 satisfactory comparison can be made, and the Eutherian orders 

 appear to differ about as much from one another as the marsupial 

 does from them. As soon as I can obtain some leisure from more 

 pressing other work, I hope to give reconstructions of the very 

 early skulls of a number of types. 



In the eutherians the most noticeable character is the large 

 size of the cochlea which, even before chondrification, is coiled, so 

 that the lower part of the capsule is always large. The orbito- 

 sphenoid cartilage extends the whole way from the nasal to the 

 auditory capsules, but is usually smaller than in the marsupials; 

 and the optic nerve passes through it. The paraseptal cartilage 

 never, so far as known, unites with the capsule behind, as in the 

 Diprotodonts. The alisphenoid cartilage is always apparently 

 present, as in marsupials; and is, as in marsupials, quite a distinct 

 cartilage originally. There is good reason to believe that it is 

 this cartilage that Parker, in his work on the pig's skull; took for 

 the palatopterygoid. The carotids in the higher mammals do 

 not pierce the basal cartilage, and nerve xii. has only a single 

 foramen. 



The Fundamental Structure of the Mammalian Skull. 



The study of the early development of the marsupial and 

 eutherian skulls leads one to differ considerably from the conclu- 



