312 



ANATOMY OF VERTEBRATES. 



and articulated, or is united, throughout its length, with its fellow 

 in the Mammal. The premaxillary, 22, is correlatively shorter in 

 the Mammal, not medially confluent nor sending off a nasal process 

 from the symphysis, as in the Bird. The maxillary, 21, is larger, 

 and the nasal process, of which the beginning is shown in 

 Struthio, is a broad and high plate in Echidna and most other 

 Mammals. The hind part of the maxillary unites with a malar, 



196 



Skull of Ostrich. 



fig. 197, 26, styliform in Echidna and some Bruta, as it is in Birds, 

 fig. 196, 26. The bone, 27, articulates with 26, but expands in 

 Echidna, as in Chelonians, as it extends backward, and applies 



Skull of Ecliidna. 



itself, in most Mammals, to close the gap in the side-wall of the 

 cranium left between 8 and 6, before articulating with the tym- 

 panic, 28 : it also developes the articular surface for the mandible, 

 29-32. This is one of the marked modifications of the squa- 

 mosal in the Mammalian class. The retroduced part or append- 

 age of the upper jaw again affords the joint to the lower jaw, as in 

 the Plagiostomous Fishes : but the common pedicle, 28, is reduced 



