I ‘ DE HENTTIONS OH EVE GLASS 3 
acters might be used in addition to those which will be made 
use of in the following brief catalogue of essential mammalian 
features, were it not for the low-placed Monotremata on the one 
hand and the highly specialised Whales on the other. Including 
those forms, the Mammalia are to be distinguished from all other 
Vertebrates by the following series of structural features, which 
will be expanded later into a short disquisition upon the general 
structure of the Mammalia. The class Mammalia may, in fact, be 
thus defined :— 
Hair-clad Vertebrates, with cutaneous glands in the female, 
secreting milk for the nourishment of the young. Skull without 
prefrontal, postfrontal, quadrato-jugal, and some other bones, and 
with two occipital condyles formed entirely by the exoccipitals. 
Lower jaw composed of dentary bone only, articulating only with 
the squamosal. Ear bones a chain of three or four separate bonelets. 
Cervical vertebrae sharply distinguished from the dorsals, and if 
with free ribs, showing no transition between these and the 
thoracic ribs. Brain with four optic lobes. Lungs and heart 
separated from abdominal cavity by a muscular diaphragm. Heart 
with a single left aortic arch. Red blood-corpuscles non-nucleate. 
The following characters are also very nearly universal, and 
in any case absolutely distinctive :—Cervical vertebrae, seven ; 
vertebrae with epiphyses. Ankle-joint “ cruro-tarsal,” i.e. be- 
tween the leg and the ankle, and not in the middle of the ankle.’ 
Attachment of the pelvis to the vertebral column pre-acetabular 
in position. . 
The Mammalia since they are hot-blooded creatures are more 
independent of temperature than reptiles; they are thus found 
spread over a wider area of the earth’s surface. As however, though 
hot-blooded, they have not the powers of locomotion possessed by 
birds, they are not quite so widely distributed as are those 
animals. The Mammalia range up into the extreme north, but, 
excepting only forms mainly aquatic, such as the Sea Lions, are not 
known to occur on the Antarctic continent. With the exception 
of the flying Bats, indigenous mammals are totally absent from 
New Zealand; and it seems to be doubtful whether those sup- 
posed oceanic islands which have a mammalian fauna are really 
' The degeneration of the hind-limb in Whales and Sirenia forbids the use of 
this character as a distinctive one on the principles advocated by the selection of 
the above list. But it would be absurd to leave out hair. 
