14 



developed from the neural arch in the class Mammalia, I have indicated them by 

 single-worded names ; having found that, although they varied much in size and a 

 little in relative position, when traced through the series, they could be identified 

 from species to species. 



The most common and constant of these processes is that which usually stands 

 out, or transversely, from the base of the neural arch, and affords a joint or a surface 

 of confluence for the rib; this I have proposed to call ' diapophysis*' : the second 

 process has a range of variety in its position from the upper part of the diapophysis 

 to that of the anterior zygapophysis, but, as it is commonly somewhere between these 

 two, I have called it ' metapopkysis^ '; the third process projects most commonly more 

 or less backwards, from the base of the diapophysis, and I have termed it ' anapo- 

 physis%\ As each of the above processes developes in some species an articular 

 surface, and as each is usually more or less oblique in position, I have called those 

 processes which more constantly support such surfaces ' zygapophyses §'. The com- 

 parative anatomy of these and other ' exogenous' processes has been the subject of a 

 previous memoir ||, because their extreme degree of variety in the Order Edentata, 

 and extraordinary development in the Armadillos and true Anteaters, render them 

 of unusual importance in the question of the affinities of the Megatherium. 



The narrow compressed base of the neurapophysis of the fifth dorsal vertebra in 

 that animal having risen above the centrum, developes on its outer surface a large 

 vertically oval articular surface, n', concave in the direction of its long axis, almost 

 flat transversely ; to which surface a corresponding convex articular surface, «", on 

 the upper part of the neck of the rib near the head, is adapted. Above the surface, 

 n', the diapophysis, d, stands out, short, thick, subdepressed, expanded at its extremity, 

 which is slightly produced backwards and supports on its outer surface an elliptical 

 articular concavity, d', with the long axis directed from above downwards and back- 

 wards, and articulated to a corresponding convexity, d", upon the tubercle of the rib. 

 A rugged tuberosity, m, on the upper and fore-part of the diapophysis represents in 

 rudiment the metapophysis. A smaller tuberosity is interposed between the anterior 

 zygapophysis, z, and the neurapophysial surface, n', for the rib. Thus the neural 

 arch of the vertebra in question presents ten distinct articulations besides the two 

 sutural ones now obliterated by its anchylosis to the centrum, which part has its two 

 large terminal articulations distinct from those for the head of the rib, d, which 

 I reckon among the neurapophysial ones. .The rib, which term I confine to the 



* Lectures on the Comparative Anatomy of the Vertebrate Animals, 8vo, Longmans, 1846, vol. i. p. 42 ; 

 from cui trans, and airwpvtru processus. 



f On the Anatomy of the Male Aurochs, Proceedings of the Zoological Society, November 14, 1848, p. 131 ; 

 from ficni inter, and uwtyvtris. 



I On the Anatomy of the Aurochs, ut supra, p. 131 ; from dyd retro, and dvtyvms. 



$ Lectures on the Comparative Anatomy of the Vertebrate Animals, p. 43 ; from Zvyov junctura, and 

 dxofvait ; these are called the " oblique or articular processes" in Human Anatomy. 



II Philosophical Transactions, 1851. 



