10 MEGALONYX. 



Mylodon, but, on the contrary, becomes narrower as in the Ai, though compara- 

 tively to a much less extent. 



Inferior View. — (PI. III.) The base of the skull of Megahnyx appears relatively 

 narrower in comparison with its length than in Mylodon. 



The occipital condyles are less sessile than those in the latter genus, and they 

 also project more downward and backward. Their articular surface is bent about 

 the middle, one-half being directed upward, backward, and outward, and the other 

 half downward, forward, and outward. 



The basilar process is relatively narrower and more uneven than in Mylodon or the 

 Ai. Between the condyles it presents a concave border, in the median line it is 

 convex, and on each side it slopes into a deep concave fossa, which is bounded ante- 

 riorly by a prominent rough protuberance, and extends postero-externally to the 

 border of the inion between the condyle and para-mastoid process. About the 

 middle of the fossa just indicated, there exists a deep oval pit or short canal formed 

 by the conjunction of two anterior condyloid foramina. Between the rough pro- 

 tuberances mentioned, the basilar surface is concave ; and anteriorly it is defined 

 from the sphenoidal body by a serrated suture, which is convex forward. 



The surface of the sphenoidal body is plane, and converges anteriorly between 

 the roots of the pterj-goid processes to an angular depression, terminating in a 

 foramen or fissure passing above the base of the vomerine articulation. 



The auditory process in the present view of the skull ajppears as a rugged V- 

 shaped portion of bone, with a tuberous apex. 



Wedged between the auditory process and a short inconspicuous para-mastoid 

 p)rocess, there exists a robust, cylindroid tuberosity terminated by a concave dis- 

 coidal surface for articulation with the stylo-hyal bone. 



Internal to the process just described, is the jugular foramen, which is large 

 and oval. Separated from the jugular foramen by a rough ridge, the carotid fora- 

 men is situated ; and in advance of this, also separated by a rough ridge, which 

 is an offset from the auditory process, there is a" deep infundibular pit constituting 

 the osseous continuation of the tympanic tube. 



Piercing the base of the stylo-hyal process, between it and the mastoid process, 

 there are two stylo-mastoid foramina. 



Looking directly at the base of the skull, the foramina ovale and rotundum are 

 nearly concealed from view by the roots of the pterygoid processes bending out- 

 wardly. Both are large and are directed forward. The former is situated between 

 the posterior part of the root of the pterygoid process and the inner end of the 

 glenoid articulation ; the latter is placed about the third of an inch in advance of 

 the other. 



The glenoid articulation is elliptical in outline, and its long diameter is directed 

 outward and forward. Antero-posteriorly it is nearly a plane, and measures about 

 fourteen lines ; and transversely it is concave, and measures two and a half inches. 



The hard palate is relatively naiTower than that of Mylodon. Between the posterior 

 three molars it is only fourteen lines wide ; and it forms a median convexity nearly 

 as prominent as the protruding portion of these teeth. 'In advance of the third 

 molars it gradually loses its convex character and expands into a nearly plane 



