28 



The haemapophyses are distinct, but short and stumpy, in the first caudal vertebra 

 of the Dasypus longicaudutus, Pr. Max. : in the Myrmecophaga jubata they present 

 proportions much more nearly resembling those in the first caudal vertebra of the 

 Megatherium, and they are equally disjoined at their distal ends*. 



The Mylodon in the number, as well as the proportions and structure of the caudal 

 vertebrae, makes the nearest approach to the Megatherium ; the haemapophyses are 

 equally distinct from each other in the first caudal*)*. 



Upon the whole, our deductions from the characters of the parts of the skeleton 

 described in the present section of this memoir, would lead to an inference that Me- 

 gatherium was nearer akin to Myrmecophaga than to Bradypus ; nevertheless the cer- 

 vical vertebrae, the condition of the anterior ribs, the form of the manubrium sterni, 

 and the pelvis, illustrate the intermediate nature of the giant's affinities, and afford 

 an additional instance to many others which I have had occasion to point out, of a 

 closer adherence to a common type in extinct animals than in the existing species to 

 which they may be most nearly allied. 



§ 4. Of the Skull. 



The skull of the Megatherium is chiefly remarkable for its small relative size, 

 especially in respect of breadth, for the slight diminution of this diameter from the 

 occiput to the end of the nasal bones, for the length and strength of the ascending 

 and descending processes from the orbital end of the zygomatic arch, and for the 

 peculiar depth of the lower jaw, especially at its middle part, where it lodges the long 

 molar teeth. 



In the skulls and portions of skulls which have come under my observation, all the 

 cranial and most of the facial sutures, save those that unite the tympanic to the rest 

 of the temporal bone, had been obliterated, and the originally complex assemblage of 

 bones forming the cranium and upper jaw had been reduced to a continuous whole. 



Viewed from behind, the skull is remarkable for the degree to which the pterygoid, 

 palatine and maxillary portions descend below the true ' basis cranii ': in consequence 

 of which, the foramen magnum and occipital condyles appear to be situated in the 

 upper half of the direct back-view, Plate XIV. fig. 1. 



The basioccipital (i) is a broad depressed plate with a thin smoothly rounded con- 

 cave posterior border : it slightly increases in thickness as it advances forwards to 

 blend with the basisphenoid (Plate XV. j), but developes on each side a rough protu- 

 berance for muscular attachments, anterior to the occipital condyles. In a side view, 

 Plate XII., these condyles form the most prominent parts of the occipital region, 

 which, as it rises above them, slopes forward, giving a very low character of intelli- 

 gence to the cranium. 



* See Philosophical Transactions, 1851, Plate LIII. fig. 60. 

 f Memoir on the Mylodon, 4to. p. 69, pi. 8, fig. 5, b, b. 



