294 



ZAGLOSSUS. 



in length up to the tune when the premaxillaries fuse dorsally, after which 

 there is practically no change in its length. The continued elongation of the 

 rostrum seems thereafter to take place by growth at its basal portion so that 

 the termination of the premaxillary is carried progressively farther forward 

 from the ventral margin of the orbit. This is in accord with the fact that the 

 sutures at the base of the rostrum are the last to close in the dorsal view of the 

 skull. Thus in a partly grown skull M. C. Z. 7,010, in which the premaxillaries 

 have fused dorsally, their extreme ventral length is 73 mm., and from the pos- 

 terior tip to the orbit is 12.5 mm. In the fully grown skull, M. C. Z. 12,415, 

 in which these sutures are still visible, the extreme length of the premaxillary 

 branch is 74 mm., practically as in M. C. Z. 7,010, but from its posterior tip to 

 the orbit is 29 nmi., indicating that later growth has been entirely at this basal 

 portion of the rostrum. The premaxilla at the same time has been carried 

 forward and a line is left in posterior continuation of the cleft into which its 

 tip fits. 



Cranial Measurements of the Proechidna. 



Two quite adult skulls have also been studied. These are of the size of 

 M. C. Z. 12,415 but show a stage farther in ossification. The first (12,414) is 

 in the collection of the Museum of Comparative Zoology; the second (22,992) 

 is in the collection of the United States national museum. In both, the sutures 

 are totally obliterated, and the crania are solid masses of bone, except that the 

 tympanic rings (wanting in 22,992) have not fused with the rest of the skull. 

 Rugosities are developed for muscle attachment on the vertex of the skull, 

 and just back of the orbit a slight ridge or process is developed on the frontal 

 which may be considered a postorbital process homologous with that of other 

 mammals. A small swelling opposite it near the anterior end of the jugal 

 defines the orbit, back of which the broad plate-like expansion of the jugal 

 covers over nearly all of the temporal fossa. The rami of the lower jaw though 



