fst 
Mar. 27, 1873] 
present the outer upper and the inner lower are rudimen- 
_ tary. The canines are absent in all ; the full complement 
of molars are present, of similar character, and degene- 
rating at either end ; they are formed on the Lophiodon 
type; the outer wall is very strong and oblique, with the 
cusps but little developed and the cingulum large be- 
hind ; the posterior transverse ridge sends forward a pro- 
* cess from near its middle, which in one fossil species 
(R. tichorhinus) is met by another from the anterior wall 
to form a circular foramen behind the anterior fossa. The 
_ lower molars agree with those of Palzotherium, being 
formed of a double crescent, in which the posterior cornu 
of the front lunule is partially overlapped by the anterior 
cornu of the hind one; no third crescent is found on the 
last molar ; three toes are present on all the limbs. They 
have not been found fossil in the Eocene strata, conse- 
quently the American species are among the earliest. 
Leidy has named an allied genus of small size Hyracodon. 
Its teeth resembled rhinoceros, but the anterior premolars 
were retained ; the peculiar cvs on the posterior trans- 
verse ridge was wanting, and the proportions of the in- 
cisors were reversed. [here are several extinct species 
of the genus Rhinoceros. Acevotherium possessed the 
same number of teeth as the Asiatic genera, but the nasal 
bones were small, slender, and smooth above, so they 
could scarcely have carried a horn ; it is a Miocene form 
only ; a fifth rudimentary toe was present. Except 2. 
pleuroceros, which had two laterally-placed tubercles on 
the nasal bones, all the other species had them median. 
They may be divided by their incisors, as are the recent 
genera, some having them rudimentary, others not. All 
the European specimers had two horns, with or without 
functional incisors, ‘Ihe English species, which are not 
peculiar, are from Pliocene and Pleistocene formations ; 
in 2. leptorhinus the nasal septum was not ossified ; in 
others it was much so, as in #. “ichorhinus, a species 
which has been fourd preserved by ice in the river Vilni, 
a branch of the Lena, in Siberia; it possessed a hairy 
coat and the peculiar pit in the molars mentioned 
above. 
From Port St. Julian, in Patagonia, Mr. Darwin first 
obtzined bones of the peculiar genus Macrauchenia, 
which has not been found out of South America, and only 
in the Pleistocene deposits there. Prof. Huxley has 
proved the existence of a second smaller species from 
some fraginents out of a copper mine in Bolivia. Owen 
showed in his, the first description of the animal, that the 
vertebrae were peculiar, and agreed with those of the 
Camels in having the vertebral artery threading a bony 
canal inside the spinal column, instead of through the 
bases of the transverse processes. It may be remarked 
that Myrmecophaga exhibits a similar conformation. 
But these vertebra in Macrauchenia are further peculiar 
in having both ends of the centra quite flat instead of 
their being opisthoccelous, as in the allied forms. M. 
Bravard, who was killed in the earthquake at Mendoza, 
left excellent drawings of the skull and other parts of this 
animal, which Prof. Burmeister has since published. 
From them we learn that the skull was not unhorselike ; 
the orbital ring was complete ; the palate was not fully 
ossified between the posterior molars (the camels present 
the same peculiarity, though Artiodactylate) ; the nasal 
bones were extremely reduced, so that the anterior nares 
were directly above the posterior, and the lower jaw had 
the angle prolonged. Burmeister thinks, and with good 
reason, that the animal possessed a fair-sized trunk. 
There were twenty-four dorso-lumbar vertebrae, of which 
seventeen were dorsal. The radius and ulna, as well as 
the tibia and fibula, were fused throughout. The femur 
possessed an extremely small third trochanter ; and there 
were three toes to each limb. The astragalus was strongly 
Perissodactylate, no cuboid facet being present. Our 
knowledge of the teeth is somewhat deficient, as they are 
_ always preserved in a much worn state. The typical 
4 
Peart Oe. ok ae eee er 
WA LORE 
409 
forty-four were present ; the incisors were equine, and the 
canines of the same size; the back molars were the 
bigger and the anterior premolars comparatively simple. 
The lower molars formed double crescents, as in Palzo- 
therium. 
In tracing back the descent of the Eguide, the Palzeo- 
therium d’Orleans of Cuvier has been shown to be gene- 
rically diferent, and has been ca'led Anchitherium ; it is 
also found in Nebraska. These were small horse-like 
animals with teeth much as in Palzotherium, forty-four in 
number ; the first premolars were very small, and no pit 
was present in the incisors ; the outer wall of each molar 
was also concave opposite the cusps; the lower molars 
formed double crescents, and the last possessed the extra 
lobe. The ulna and fibula were fused with the radius and 
tibia respectively ; the astragalus had some of the ob- 
liqueness of that of the horse, which it resembled in 
many other points. But there were three toes on the 
limbs, the lateral ones being less strong than the median. 
A peculiar antorbital fossa was present. 
The horse must be described before the affinities of its 
close allies can be realised. In it the incisors possess the 
well-known pit ; the canines are rudimentary in the mare; 
the premolars resemble the molars, and the crowns are 
very long and deeply embedded, with a concave crescent 
opposite the tubercles on the outer wall and the anterior 
internal tubercle insulated at first; otherwise they are 
typical. The depressions are very deep and are filled up 
by cementum, to form a solid mass. The lower molars 
are slightly complicated double crescents. The ulna and 
fibula are not free. H/ipparion had very horse-like teeth. 
Itis a later Miocene form, and is common in the New and 
Old World. It possessed the antorbital pit, as in Anchi- 
therium, but was otherwise very equine. The canines 
were present in both sexes of equal size, and the anterior 
internal tubercle of the molars was completely insulated. 
The median of the three digits alone was functional. 
Merychippus, a Pliocene form, recognised by Leidy from 
some teeth, seems to have been an intermediate form 
between these and Anchitherium. Fossil true horses 
abound in America as well as the Old World ; they since 
became extinct in the former locality. They are found in 
the Pleistocene nearly everywhere ; their earliest remains 
are from the Sevalik Hills. 
With these animals the description of the fossil Peris- 
sodactylata terminates. 
PERCEPTION IN THE LOWER ANIMALS 
oS on this interesting subject still continue to 
pour in upon us in so great abundance that limited 
space compels us to select merely the facts contained in 
each. The best service we can at present render to the 
unravelling of the, we think, yet unsolved problem is 
simply to accumulate facts; no doubt a satisfactory ex- 
planation will by-and-by be arrived at. First we must 
give place to Prof. Croom Robertson, who thus writes as 
to the theory broached in his former letter :— 
In my former letter I made no pretension to explain all the 
wonderful feats reported of dogs or other animals, but only 
argued, in the wake of Mr. Wallace, that it had never been 
sufficiently considered what help in finding their way dogs might 
have from smell alone. Be the help what it may in the parti- 
cular cases, I thought it clear that, if in their common experi- 
ence smell does not somehow supply to dogs the defect of touch, 
they are, as far as we can see, badly fitted out, by comparison 
with men, for making their way through the world. And, even 
after your article of last week, I must still in their interest hope 
that the notion of a continuous world of smells is not an impos- 
sible one, 
If the external world were the same to dogs that it is to men— 
a complex of interwoven touches and sights in space, and only in 
addition dogs had more frequent and varied experiences of smell, 
the dying away or shifting of some in a particular train of odouis 
would doubtless, as the writer of the article urges, put a dog out 
