40 DESCRIPTIONS OF PREPARATIONS. 



the latter than to the former of these two sets of Mammalia, and that even as 

 regards the particular difference, such as it is, which exists between claws and 

 hoofs, the subungulate character of certain South American Rodents (Dasyprocta, 

 Caelogenys, Dinomys, Cavia, Dolichotis, and, notably, Hydrochaerus) very much 

 reduces its value. The fact pointed out in the Description of Preparation, p. 27, 

 note, to the effect that the microscopic character of the ultimate radicles or spon- 

 gioles of the lacteal system in the Rabbit resembles that of the Ruminants rather 

 than that of the Unguiculata, illustrates this position. On the other hand, however, 

 Krause, Hdbk. der Menschlichen Anatomic, p. 234, 1876, has pointed out that 

 the Rabbit, unlike the Ungulata, Horse, Pig, Ox, and Sheep, has capillary veins in 

 the spleen instead of wide funnel-shaped orifices for the commencement of those 

 vessels. The semi-pedunculate fashion in which the deciduous serotina is in the 

 Guinea Pig, Agouti, and some other Rodents, attached to the wall of the uterus, 

 and the fact that in the former at least of the animals named this structure is 

 sometimes retained within the uterus at parturition, may appear to point to the 

 existence of some approximation to the character of the non-deciduate cotyledonary 

 placentation of typical Ruminants. But the springing up in later foetal life of a 

 zone of villi, supplied by omphalo-mesenteric vessels around and exteriorly to the 

 placental area in Rodents, though of physiological interest, as was pointed out in 

 the Zoological Transactions for 1863, vol. v, still does not constitute, as seems to 

 have been more recently stated, any but a physiological approximation of the 

 Rodent to the Ruminant type of placentation. 



The peculiarity of the placentae of the Guinea Pig and Agouti just alluded to, 

 the comparative simplicity of their caecum, and the great development of the 

 spirally-coiled portion of their colon, and the presence in them o but a single 

 superior cava, the small number of their mammae and of their young, and the 

 early attainment by them of the faculty of self-help, are points in which they 

 resemble the Artiodactyla and differ from the LagomOrphi but, as the Descriptions 

 of the Preparations (Nos. 3 and 4) show, Brandt is entirely justified in pointing, 

 I.e. p. 291, to numerous connecting links, characteribus nonnullis generis Leporini 

 cum Ruminantium ordine. 



The apparent paradox of an affinity connecting the Proboscidea (the Elephant 

 and Mastodon) with the living Rodents, has already been alluded to, p. 8. One 

 of the most striking of these resemblances lies in the facts that in both sets of 

 animals the intermaxillary interposes itself between the maxillary and the nasal 

 bones and joins the frontal without however touching upon the lacrymal bone, 

 relations which do not exist either in the Aye-aye, or in the Hyrax, or in the 

 Dugong, animals with incisors of somewhat similar relative proportions. But this 

 remarkable peculiarity had not been attained to by the Pliocene genus and sub- 

 order Glires hebetidentati of Alston, represented by the Mesotherium, in which 

 animal the intermaxillary's nasal process is too short to prevent the maxillary from 

 abutting upon the nasal, and fails, as in Hyrax alone of the animals just mentioned, 

 to reach the frontal. 



The absence of enamel from the incisor teeth or tusks of the adult Elephant, 

 otherwise so exactly homologous with the incisors of the Rodents, might appear to 

 constitute a difference between them and those of the Rodents, did we not know 

 that these teeth when first cut in the Elephant have a cap of enamel, and that a 



