23 



depressed broad process with a rough free extremity ; the back part of the process 

 coalesces with a similar but stronger and longer diapophysis of the fifth sacral, d*, 

 from the fore-part of the base of which a tuberous metapophysis, m 5, projects upward 

 and forward. The third, o 3, and fourth, o 4, upper sacral outlets are wider apart than 

 the second and first; the sacrum expanding posteriorly. The back and under part 

 of the diapophysis of both the fourth and fifth vertebrae coalesce with the ischium 

 and with the thick and strong parapophysis extended from the side of the centrums. 

 The neural arch of the fifth sacral developes a pair of posterior zygapophyses, Plate 

 VII. z', z', with a flat surface looking outward and a little downward, and with the 

 lower angle continued upon a small rough subarticular surface. The posterior 

 surface of the last sacral vertebra, Plate VII. fig. 2, is on the same vertical parallel 

 as the posterior zygapophyses ; it is nearly flat and transversely elliptic. The neural 

 canal of the sacrum, the anterior aperture of which is 3 inches in vertical and 4 inches 

 in transverse diameter, expands in the sacrum, and opens below by three wide fora- 

 mina on each side: of these the first and second are of great size: into the second 

 foramen the third upper sacral canal leads: the third lower sacral foramen, which 

 is the smallest, corresponds with the fourth upper one: the fifth canal for the fifth 

 pair of sacral nerves broadly grooves the back part of the parapophysis and side of 

 the centrum. The posterior aperture of the neural canal is 2 inches in vertical and 

 4 inches 3 lines in transverse diameter. Both diapophyses and parapophyses of the 

 first three sacral vertebrae coalesce with the ilia. The sacrum is concave below both 

 transversely and lengthwise. 



The tail of the Megatherium was of great strength : it is so long as to touch the 

 ground when the trunk is raised at an angle of forty-five degrees from the horizontal 

 position : it includes eighteen vertebrae, which progressively diminish in size from the 

 first to the last, Plate I. C d, 1-18. 



The first vertebra, Plate II. fig. 2, is remarkable for the length and strength of its 

 diapophyses, d, which are expanded at both ends, and, like those of the sacral verte- 

 brae, are probably lengthened out by connate or coalesced pleurapophyses, pi. The 

 base of the process, dp, extends from the side of the centrum to the base of the neural 

 arch, is widely excavated behind for the passage of the first pair of caudal nerves, 

 and is subcompressed before it expands into its rugged free termination. These pro- 

 cesses are shorter than those of the last sacral vertebra. The neural canal, n, is tri- 

 angular, 3 inches in vertical and 3 inches 9 lines in transverse diameter. The neural 

 arch developes two posterior zygapophyses, z 1 , with their articular surfaces looking 

 downwards and outwards: two anterior zygapophyses, z, with their articular sur- 

 faces looking upwards and inwards, these being strengthened by a strong tuberous 

 metapophysis, m, on their outer side: the spine, ns, is of moderate length, carinate 

 behind, obtuse and slightly expanded above. From the under part, of the trans- 

 versely elliptical centrum are developed two hypapophyses, hy, each with an oblong 

 articular surface, Plate X. fig. 6, hy, to which is joined a haemapophysis, Plate II. //. 



