FOSSIL MAMMALIA. 



29 



form of Rodent is peculiar, should be found to contain the remains of an extinct 

 genus, characterized by a dentition which closely resembles the Rodent type, but 

 manifesting it on a gigantic scale, and tending to complete the chain of affinities 

 which links the Pachydermatous with the Rodent and Cetaceous Orders. 



arches 



condyle 



ADMEASUREMENTS OF THE CRANIUM OF TOXODON. 



Extreme length 



Extreme breadth 



Extreme height, (exclusive of the lower jaw) 



Length of zygomatic process 



Depth or vertical extent of do. . 



Transverse extent of zygomatic fossa . 



Transverse diameter of cranium between the zygomatic 



Transverse diameter of occipital plane of the cranium 



From the outside of one condyle to that of the opposite 



Length of the bony palate 



Extreme breadth of ditto .... 



Breadth of palate at the intermaxillary suture 



Do. do. behind the molar alveoli 



Longitudinal extent of the molar alveoli 



Do. do. diastema . 



Transverse diameter of posterior nasal aperture 



Do. do. of occipital foramen 



Do. do. of glenoid cavity . 



Antero-posterior do of ditto 



feet inches lines 

 2 4 

 14.. 

 ... 10 

 1 1 6 



DESCRIPTION OF FRAGMENTS OF A LOWER JAW AND TEETH OF A TOXODON. 

 Found at Bahia Blanca, in latitude 39° on the East coast of South America. 



In looking over some fragments of jaws and teeth, forming part of Mr. Darwin's 

 collection of South American mammiferous remains', and which had been set 

 aside with mutilated specimens referrible to species belonging to the family of 

 Edentata, my attention was caught by the appearance of roots of teeth project- 

 ing, in a different direction from the grinders, from the fractured anterior ex- 

 tremity of a lower jaw, and I was induced to examine minutely the structure 

 of the teeth in this specimen, and to search the collection for corresponding 

 fragments. The result was the discovery of portions of the two rami, and the 

 commencement of the symphysis of a lower jaw, containing anteriorly the roots of 



