II LEMURS AND THEIR YOUNG 19 
teat_ would of course be absolutely incomparable with a mammary 
pouch, because in that case the wall of the teat itself would be 
the pouch. 
Mammals belonging to quite different Orders show traces 
more or less marked of a marsupium. In young Dogs the teats 
are borne upon an area where the skin is thinner, the covering 
of hair less dense than elsewhere—all points of resemblance to 
the inside of the pouch of a Marsupial; in addition to this 
there are traces of the sphincter marsupii muscle. In other 
Carnivora there are similar vestiges. In Lemur catia a more 
complete rudiment of a marsupial pouch is to be met with. In 
this Lemur the teats are both inguinal and pectoral; the skin 
in these regions is thin and but slightly hairy, and extends 
forwards as two bands of the same thinness and smoothness on 
each side of the densely hairy skin covering the sternum. This 
area is sharply separated from the rest of the integument by a 
fold which runs parallel to the longitudinal axis of the body, 
and can be comparable with nothing save the rudiment of the 
marsupial fold. 
One is tempted to wonder how far the habit which certain 
Lemurs have of carrying their young across the abdomen with 
the tail wrapped round the body of the mother is a reminiscence 
of a marsupial pouch. 
Skeleton. 
The skeleton of the Mammalia consists almost solely of the 
endoskeleton. It is only among the Edentata that an exo- 
skeleton of bony plates in the skin is met with. As in other 
Vertebrates, the skeleton is divisible into an axial portion, 
the skull and vertebral column, and an appendicular skeleton, 
that of the lLmbs. The bones of mammals are well ossified, 
and in the adult there are but few and small tracts of cartilage 
left. 
Vertebral Column.—The vertebral column of the mammals, 
like that of the higher Vertebrata, consists of a number of 
separate and fully-ossified vertebrae. 
The constitution of a vertebra upon which all the usual 
processes are marked is as follows:—There is first of all the 
body or centrum of the vertebra, a massive piece of bone shaped 
like a disc or a cylinder. The centra of contiguous vertebrae 
