Muscles and Nerves 189 
into an icy mass, the high temperature of the bird being 
of itself insufficient to obviate this, although assisted 
by the great development of the subcutaneous fatty 
layer, which far exceeds in thickness that of the corre- 
sponding structure in the member of any other group 
of birds, and recalls to mind the fatty deposit of ‘blub- 
ber’ of the seals and cetaceans.” 
When we looked at the blood of a bird, we saw the 
tiny white corpuscles, which in life flow and move in 
every direction, constantly changing their outline; and 
now if we take a piece of a bird’s muscle or flesh and 
examine it carefully, after ‘teasing’ it out into shreds 
with a needle, we shall see another kind of cell-animal. 
These are long and generally pointed, each a single cell 
with a tiny spot or nucleus in it, differing from the white- 
blood animals in being able to stretch out and contract 
in only one direction. When we will our arm to close 
together, bringing our hand close to our shoulder, a thick 
colony or bunch of these muscle-animals shortens, be- 
comes stouter, and bulges up under the skin on our upper 
arm. 
In our own body the bones of the spinal column are 
movable, and we can bend in almost every direction, 
and so we are provided with many important back-muscles. 
But if we have ever carved a chicken, we shall remem- 
ber that the ribs and shoulder-bones are close to the sur- 
face, and but poor pickings are to be had from them. 
The breast and chest, on the contrary, are hidden in a 
thick mass of muscles, most of which are concerned with 
moving the wings in flight. The immense pectoral or 
