DE. CAEPEXTEE’s ZOOLOGY. 
51 
the appearance and number of the different vertebrae, &c., &c. Too 
much importance would seem to be attributed by many to purely his¬ 
tological characters. Professor Owen thus concludes his remarks on this 
portion of the subject:— 
“ There are few characters of the osseous system common, and at the same time pe¬ 
culiar, to the class Mammalia. The following may be cited :— 
“ 1. Each half or ramus of the mandible consists of one bony piece developed from a 
single centre: the condyle is convex or flat, never concave. This has proved a valuable 
character in the determination of fossils. 
“ 2. The second or distal bone, called ‘ squamosal,’ in the bar continued backwards 
from the maxillary arch, is not only expanded, but is applied to the side wall of the 
cranium, and develops the articular surface for the mandible, which surface is either 
concave or flat. (The Wombat is, perhaps, the sole exception to this rule.) 
“ 3. The presphenoid is developed from a centre distinct from that of the basisphenoid. 
“ In no other class of vertebrate animals are these osteological characters present.” 
The dental apparatus in the Mammalia is next noticed by Professor 
Owen, who in the short limits of five pages furnishes us with a concise 
though admirable summary of the different characters which it presents; 
characters which (as Professor Owen himself observes) “have not been 
clearly or accurately defined in any systematic or elementary work on 
Zoology, although an accurate formula and notation of the teeth are of 
more use and value in characterizing genera in this than in any other 
class of animals.” The possession of the information contained in this 
portion of Professor Owen’s article seems to us to be indispensable to 
every zoological student. 
Having made these preliminary observations, Professor Owen then 
proceeds to the discussion of the main subject of his inquiry, namely, 
the true principle on which the primary divisions of the class Mam¬ 
malia should be founded. Various attempts have from time to time 
been made to determine this important question. The first system 
which deserves notice is that of Aristotle, who founded his classification 
on the principal modifications presented by the locomotive system. The 
Mammalia or Zootoka were by him divided into three sections: 1st, 
Dipoda, or Bipeds; 2nd, Tetrapoda, or Quadrupeds; and 3rd, Apoda, 
or Impeds. The Tetrapoda are divided into those with claws and those 
with hoofs. The unguiculate quadrupeds are again subdivided accord¬ 
ing to the nature of their teeth; the ungulate quadrupeds according to 
the divisions of their hoofs, as, e. g., into Polyschidse, or multungulates, 
Dischidse, or bisulcates, and Aschidse, or solidungulates. Professor Owen 
remarks that “this, in most respects admirable system, would have 
commanded greater attention, and been now recognised as more mani¬ 
festly the basis of later systems, had its immortal author more technically 
expressed his appreciation of the law of the subordination of characters; 
but he applies to each of his groups, whatever their value, the same de¬ 
nomination, viz., genos.or genus.” 
By Cuvier the Mammalia were subdivided according to the charac¬ 
ters presented by the generative, locomotive, osseous, and dental systems, 
too much importance being in some instances attached to the latter. 
