510 DE. C. I. FOKSTTH MAJOR ON 



The "peroueum" would then be homodynamous with the ulnave externum Thil. 

 (ulnar part of Pfitzner s triquetrum bipartitum),=V 2; and tlie vesalianum tarsi with 

 the vesalianum cai'pi,=V3, or tarsale 5, the cuboid being tarsale 4. 



The cuboid of jMammalia is generally considered to be a compound of tarsale 4 + tarsale 

 5 ; but where an os vesalianum, or its traces on the tuberosity of Metat. V, are present 

 such a supposition cannot, however, be admitted. Emery found in embryos and poucli 

 specimens of the Marsupial genera Didelphys, JEpyprnmnus, and Phascolarctm separate 

 tarsalia t and 5 *. Por the former genus at least he has demonstrated that tarsale 4 

 and tarsale 5 become fused in later stages. This instance of a compound Mammalian 

 cuboid (tarsale 4 and 5) is the only one in the literature which can be taken seriously ; 

 but it is quite possible that in other Mammalia too the vesalianum uiay be assimi- 

 lated by the cuboid, instead of by Metat. V, as in Man and some Rodeutia. 



Concluding Remarks and Suggestions as to Classification. 



The oldest known lagomorjihine genera, Titanomys, and Falceolagas, have several im- 

 portant characters in common : still, the differentiation into Lagomyidoe {Titanomys) and 

 Leporida3 {FalcBolcigus) had already taken place. In the number of upper molars and in the 

 shape and composition of the bony palatal bridge, Titanomys shows itself the precursor of 

 the recent Lagomys, Palopolagus of the recent Lcpus ; and it is therefore advisable to retain 

 the two groups as families, although they converge back in time. Moreover, in other 

 characters — absence of su])raorbital processes, pattern of the cheek-teeth — Palceolagiis 

 approaches nearer the Lagomyidse than do the more recent Leporid;e. In the gradual 

 transformation of their cheek-teetli, both groups, as has been amply demonstrated, run 

 parallel from the Lower Miocene down to recent times. The Lagomyidtii, as at present 

 known, start from a more primitive type than the Leporidae, since in Titanomys the 

 cheek-teeth have remnants of roots and the upper ones preserve their original pattern 

 throughout life ; whereas in Tahcolagiis, so far as I know, the cheek-teetli are already 

 rootless, and in old age they lose their original pattern, without, however, developing the 

 new one. In the transformation of their tooth-pattern the Leporidae eventually go a step 

 beyond the point at which the Lagomyida? stop, the cheek-teeth of Lepus being more 

 completely metamorphosed than those of recent Lagomys. In this respect, as well as in 

 the specialization of their limbs for swiftness, correlated with the greater perfection of the 

 sense-organs — and, as a consequence, witli corresponding modifications of the skull — 

 the Leporidte are to be considered the more specialized of tlie two ; but there are several 

 members of the Leporidae which, with regard to the two last-mentioned sets of characters, 

 and the complete or almost complete absence of the tail, preserve considerable similarity 

 to the Lagomyidte. By the absence of the upper m. 3, and by some peculiarities of 

 the cranium, pointed out by Winge (perforation of the fossa pterygoidea — fusion of the 



* Atti Ace. Liiicei, Eend. iv. 2, p. 274 (IS&iJ) ; id. in Semon's ' Forschuiigsreiseii in Australien,' &c., ii. pp. 374, 

 378, 383; figs. 20, 30, 31, 59 (1807). 



