il E G A L O X Y X . 



13 



The upper part of the face is shorter, and broader, and anteriorly is less sloping. 



In the present specimen the palatine canals become exposed and form a deep, 

 concave, trilateral fossa situated just in advance of the middle of the position of 

 the hiatus separating the first from the back molars. (PL YI, Fig. 1.) The antero- 

 interual angle of the fossa is continuous with a shallow groove passing to the inci- 

 sive foramen; and the autero-external angle communicates with a large canal 

 ascending at the postero-internal side of the alveolus for the first molar. In Dr. 

 Owen's specimen the shallow groove proceeding to the incisive foramen, is derived 

 from a foramen communicating with the palatine canal. 



The alveolus for the first molar is not so deep as in Dr. Owen's specimen ; and 

 its bottom does not reach within half an inch of the position of the anterior orbital 

 margin, but this difference is jirobably dependent upon age merely. 



ComiMvative Measuremenls of the Skulls o/Megalontx Jeffersonii in the Collections 

 of Drs. Oicen and Dickeson. 



Length of the skull from the occipital condyles to the ante 



rior margin of the first molar alveoli 

 Length of temporal fossa to post-orbital protuberance 

 Depth of temporal fossa in a straight line . 

 Length of face from post-orbital protuberance 

 Height of face from most prominent part to middle of hard 



palate ....... 



Breadth of face at post-orbital protuberances 



Breadth of face at anterior extremity . 



Breadth of face at sides of first molar alveoli 



Height of face at anterior extremity . 



Diameter of orifice of the nose . 



Length of face from the first to the last molar alveolus 



Breadth of cranium at narrowest part of the temporal region 



Length of sagittal crest ...... 



Height of inion from inferior margin of occipital foramen 

 Breadth of inion at mastoid processes 



De. 



Owen's 



Dr. Die 



keson's 



SPECIMEN. 



SPECIMEN 





Dche 



s. Lines. 



Inches. 



Lines. 



14 





13 



3 





1 



9 



7 



9 





4 





4 



6 





4 



8 



4 



5 





6 





5 



9 





4 



11 



5 



5 





3 



9 



3 



9 





4 



6 



4 



6 



estimated. 



5 





5 







3 



6 



3 



6 





1 





6 



9 



estimated. 



3 



G 



4 







5 





5 







4 



4 



4 



4 





6 



3 



6 



6 





Inferior Maxilla. — (PI. I, V.) The illustrious comparative anatomist of England, 

 Professor Owen, has described, in the voyage of the Beagle (Mammalia, Pt. I, p. 

 99 ; PI. xxix), a lower jaw which he attributes to the Mecjalonyx Jeffersonii. The 

 specimen was discovered in South America, and Professor Owen remarks : " It is 

 the only fossil brought home by Mr. Darwin, that could be confidently referred to 

 the genus Megalomjx; but the form of the jaw fully justifies this determination." 



The author further observes : " The forms of the alveoli are best preserved in 

 the right ramus ; the first is the smallest, and seems to have contained a tooth of 

 which the transverse section must have been simply elliptical ; the second tooth is 

 likewise laterally compressed, but the transverse section is ovate, the great end 

 being turned forwards ; the third socket presents a corresponding form, but a larger 



