514 



NATURE 



[April 2"], 1876 



remarkable for the exceedingly small size of the brain 

 cavity, compared with the arches and ridges of the skull de- 

 veloped for muscular attachments. This character has been 

 supposed to indicate marsupial affinities, but the rest of 

 the osteology, as far as known, does not favour this view. 

 The lower jaw has not been found, but the cranium shows 

 the full complement of teeth so frequent in Eocene 

 mammals. There are three broad tubercular molars 

 behind the trihedral sectorial, which indicate that the 

 animal was rather omnivorous than truly carnivorous 

 in its habits. Another genus which includes many 

 species of various size, and having a wide geo- 

 graphical range, being found in late Eocene and early 

 Miocene deposits in France, Germany, England, and 

 North America, is called Hyccnodofi. It also has been by 

 many naturalists placed among the marsupials on account 

 of the pecuharities of its dentition, which is certainly 

 without parallel among placental Carnivores. It possesses 

 the primitive or typical dental formula of the Eocene 

 mammals, and the incisors, canines, and premolars, are 

 not unlike those of a dog, but the three true molars, both 

 above and below, are shaped like the sectorial teeth of a 

 cat or hytcna, and increase in size from the first to the 

 last, and thus there are no teeth formed like the " tuber- 

 culars " of ordinary Carnivores. This repetition of the secto- 

 rial character in the true molars occurs in the carnivorous 

 marsupials, though the general structure of the skull, and 

 limb bones as far as they are known, including the posi- 

 tion of the lachrymal canal within the orbit, will not permit 

 our placing Hycenodon in that group. Many of the lately 

 discovered American Eocene cam ivorespresented the same 

 peculiarity of several successive molars having sectorial 

 characters. One of these from Wyoming, apparently 

 allied to Hyasnodon, has been described by Cope, under 

 the name of Mesonyx, and another still more aberrant 

 form, as Synoplotherium. The inferior canines project 

 forwards, and are closely approximated, the incisors (at 

 all events in the aged specimen on which the genus was 

 founded) being absent. The molar teeth were so much 

 worn that their characters cannot be satisfactorily made 

 out. The most interesting features of these animals are 

 in the structure of the feet, the ungual phalanges being 

 flatter and broader than in any existing Carnivora, and 

 grooved above, and the scaphoid and lunar bones of the 

 carpus not being united as in all existing Carnivores. 



These naturally lead to the consideration of some ani- 

 mals, the remains of which have been discovered in the 

 same locality and formation, of such anomalous construc- 

 tion, that they cannot be placed in any of the known 

 groups, and for which Prof. Marsh has constituted the 

 order Tillodontia. The type of the order Tillotherium, 

 Marsh, is described as having a skull with the same 

 general shape as in the bears, but in its structure resem- 

 bUng that of Ungulates. The molar teeth are of the 

 Ungulate type, the canines are small, and in each jaw 

 there is a pair of large scalpriform incisors faced with 

 enamel, and growing from persistent pulps, as in Rodents. 



The adult dentition '^s i - c~ p^ m^. The articulation 

 2123 



of the lower jaw with the skull corresponds to that in 

 Ungulates. The brain was small and somewhat convoluted. 

 The skeleton most resembles that of Carnivores, especially 

 the Ursidce, but the scaphoid and lunar bones are not 

 united, and there is a third trochanter on the femur. The 

 radius and ulna, and the tibia and fibula, are distinct. 

 The feet are plantigrade, and each had five digits, all 

 terminated by long, compressed and pointed ungual 

 phalanges, somewhat similar to those in the bears. 

 Judging from the figures and description, this animal is 

 the same as that of which a lower jaw was previously 

 described by Leidy as Trogosus castoridens, and which is 

 perhaps identical with Anchippodus riparius, described 

 by the same naturalist at a still earlier date, from a single 

 tooth from New Jersey. If this identity can be satisfac- 



torily established, the latter name must be adopted, but as 

 the lower molars of so many very different animals bear a 

 close resemblance to each other, it is not very easy to 

 do so, and the whole history is a good illustration of the 

 inconvenience that often arises from the practice of giving 

 names to minute and isolated fragments. 



In some of its dental and osteological characters, Tillo- 

 therium or Anchippodus bears some resemblance to the 

 Rodentia, but the definition of that order would have to 

 be widened considerably before it could be admitted 

 within its bounds. Mcsothcriutn, spoken of in the third 

 lecture, has better claims to be considered a Rodent, 

 though certainly a very aberrant one. Lowing this animal 

 aside, palaeontology tells us nothing of connecting, or even 

 of more greatly generalised forms of Rodents, or affords 

 any better indications of the affinities of the order than 

 can be derived from the study of its living members. 

 Nearly all the existing families have been wcU repre- 

 sented throughout the Pliocene and Miocene epochs, and 

 the earliest known Rodents, those of the Upper Eocene, 

 do not appear to have been more generalised than the 

 existing species. 



Numerous species of extinct Insectivora have been 

 described from various formations from the Upper Eocene 

 to the present time, both in Europe and America., but 

 their characters and affinities have not been thoroughly 

 worked. The European species mostly belong or are 

 allied to genera now existing. It has been suggested that 

 some of the generalised Amerian Eocene Carnivores may 

 possibly be gigantic Insectivora, though in the actual 

 fauna of the world there are no connecting links between 

 these orders. It is also not certain whether some of the 

 mammals of the Mesozoic strata may not be placental 

 Insectivores. 



The Chiroptera, or bats, differ strikingly from all other 

 mammals in the adaptation of the fore-limbs as organs of 

 true flight. Their origin is an extremely interesting 

 question to the evolutionist. No existing forms throw 

 any light upon it, and what little is known of the past 

 history of the order shows that its general characters and 

 geographical distribution have not changed materially 

 during the Tertiary period. All the bats found fossil in 

 the Brazilian caves resemble those now inhabiting the 

 same country, though it is true these only go back as far 

 as Pleistocene ages. In France, however, remains of 

 bats have been found in the Miocene and Upper Eocene 

 (Paris gypsum), but all belonging to the Vespcrtilionina 

 and Rhinolophidce, families now existing in Europe, and in 

 the eariiest known forms no signs of generalisation have 

 been detected, nor have any of the intermediate stages 

 between the ordinary mammal and the bat, if they ever 

 existed, yet been discovered. No fossil remains of the 

 large fruit-eating bats, or Pteropi have been found. 

 {To be continued.') 



PROF. HUXLEY'S LECTURES ON THE EVI- 

 DENCE AS TO THE ORIGIN OF EXISTING 

 VERTEBRATE ANIMALS^ 



V. 



WE saw in the last lecture that the differences between ■ 

 birds and reptiles were very great ; nevertheless, 9 

 many of them tend to disappear on a closer examination. ^ 

 For instance, the extremely avian character of the absence 

 of teeth, and the presence of a horny beak, is found in 

 turtles and tortoises ; that of the penetration of the bones 

 by air cavities exists in the skull of crocodiles ; and, 

 although no existing reptile possesses the power of flight, 

 or a fore-limb in any way approaching in structure to a 

 bird's wing, yet, in the crocodiles, the fourth and fifth 

 digits — those we found to be wholly absent in the bird — 

 are much smaller than the others, and have no claws. 



' A course of six Isctures to working men, delivered in the theatre of the 

 Royal School of Mutes. Lecture V., March a/. Continued from p. 469. 



