Muscles and Nerves 193 
wavy cross-lines, or striations, on those which are moved 
voluntarily, such as the muscles of the neck or wing; 
but those which are moved involuntarily, as the gizzard, 
are smooth and without the cross-lines. 
Fic. 142.—Amazon Parrot in sleeping position, hanging by its toes; illustrating 
the wonderful strength of the tendons. 
Among birds new muscles have appeared, or old ones 
have split up or so changed in position that it is all but 
impossible to compare them, muscle for muscle, with other 
