10 Prof. Owen on the Class Mammalia. 7 
are provided with movable cartilages and muscles, and the ex- — 
tent of the internal organ is increased by accessory cavities or 
sinuses which communicate with the passages including the tur- 
binated bones. a 
There are few characters of the osseous system common, and 
at the same time peculiar, to the class Mammalia. The following © 
may be cited: " 
1. Fach 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 
etermination of fossils. ta 
2. The second or distal bone, called “‘squamosal,” in the bar — 
continued backwards from the maxillary arch, is not only ex- 
anded, but is applied to the side-wall of the cranium, and 
evelops the articular surface of the mandible, which surface is 
either concave or flat. 
3. The 
that of the basisphenoid. 
_ In no other class of vertebrate animals are these osteological — 
characters present. ; 
e cancellous texture of mammalian bone is of a finer and 
unsupported by more obvious and constant ones, in the inter 
pretation of a fossil. a 
_ Dental characters—The Mammalia, like Reptilia and Pisces, 
include a few genera and species that are devoid of teeth; the 
true ant-eaters (Myrmecophaya), the scaly ant-eaters or pangolins — 
« 7 
(Manis), and the spiny monotrematous ant-eater (Hehidna), a 
presphenoid is developed from a centre distinct from 
4 | 
: 
q 
examples of strictly edentulous Mammals, The Ornithorhyncbus — 
"1 
the upper jaw-bones; one of these becomes developed into. 
name of its genus Monodon. : 
‘The examples of excessive number of teeth are presented, 1 
the order Bruta, by the priodont Armadillo, which has ninety 
eight teeth: and in the Cetaceous order by the Cachalot, which 
has upwards of sixty teeth, though most of them are con ed 
to the lower jaw; by the common Porpoise, which has be 
eighty and ninety teeth; by the Gangetic Dolphin, which 
one hundred and twenty teeth; and by the true Dolphins ( 
