52 MEGATHERIUM. 



remains of the spinal arch four and a half inches in the span between the posterior 

 articular processes. 



5. Two fragments of ribs measuring three and a quarter and three and a half 

 inches in breadth at the distance of six inches from the tubercle. 



6. The head of a femur, six and a half inches in diameter at the base. 



7. The proximal extremity of a tibia and a small fragment of a second. The 

 shaft is prismoid, and at the distance of ten inches below the head of the bone is thir- 

 teen and a half inches in circumference. The head is ten and a half inches broad, 

 and measures about half as much antero-posteriorly. As in Megalonyx, the femoral 

 articular facets are separated from each other posteriorly by a concave notch, and 

 partially overhang the posterior surface of the shaft. They are separated from each 

 other by an interval of two and a half inches in width. The internal facet is"oval, 

 deeply concave, five and a half inches antero-posteriorly and obliquely, and four and 

 three-quarter inches transversely. The outer facet is antero-posteriorly moderately 

 convex, ovate in outline, five and three-quarter inches in its long diameter, and three 

 and a quarter in its short diameter. 



8. A mutilated os calcis ; an occipital condyle three and a quarter inches in its long 

 diameter, and two and a half in its short diameter ; and several fragments of teeth. 



Proceeding next with a description of the specimens of Megatherium remains 

 borrowed from the National Institute collection, that of the temporal portion of a 

 cranium consists of the temporal bone with contiguous co-ossified portions of the 

 occipital and parietal bones (PL XV, Fig. 3) ; and it corresponds in form with the 

 same part of the cranium of Megalonyx. 



The temporal surface is strongly reticulated with ridges, and is pierced with 

 numerous large vascular foramina. The parietes of the cranium in the position of 

 the squamous portion of the temporal bone at their thinnest point are an inch and a 

 half^thick; and the cranial tables are occupied with a dense intervening diploic 

 structure. 



The lateral border of the inion is a thick obtuse ridge expanding below into the 

 root of the zygomatic and mastoid processes. The zygomatic process has the same 

 inclination of its root as in Megalonyx; and the mastoid process is relatively 

 shorter, broader, and more rugged than in the latter animal. 



Back of the mastoid process is a deep gutter descending from the margin of the 

 inion above the process to the stylo-mastoid foramen. 



The entrance of the external auditory meatus is nearly on the same plane with 

 the outer surface of the zygomatic root, instead of being situated at the bottom of 

 a wide arch as in Megalonyx. Its upper boundary is prominent and rough ; and 

 the auditory process is a thick, irregular ridge extending from the outer extremity 

 of the glenoid articular cavity to the apex of the mastoid process. The meatus is 

 demi-cylindroid in form and two inches in length. 



The glenoid articular cavity is a deep, transversely oval concavity, measuring 

 two and a half inches wide, and an inch and a half antero-posteriorly. 



The specimen of a hard palate, from the National Institute collection, on its two 

 sides gives the entire length of the upper molar series as eight inches. The width 

 of the palate between the first pair of molar alveoli is thirty-four lines, and that 



