on_ ridge a fanciful resemblance to the pinion, and
in the angular shape of the _coracoid_ process to the neck and head of a
raven in full flight. Following with his finger the triangular outline
of the bone, he went on to explain how its freedom of movement is due to
its singular independence; laid loosely on the flat muscles behind the
upper ribs, it moves with absolute freedom, backwards and forwards, up
and down, unconnected with any other bone, till, turning the corner of
the shoulder, it is hinged rather than tied to the collar-bone; the
collar-bone itself free to move upwards from its articulation in the
sternum. And then talk of the great works of man! Talk of Brunellesco
and his cupola, of the engineers of the Duke of Calabria! Look at the
human arm: what engineer would have dared to fasten anything to such a
movable base as that? Yet an arm can swing round like a windmill, and
lift weights like the stoutest crane without being wrenched out of
its sockets, because the muscles act as pulleys in four different
directions. And see, under the big _deltoid_, which fits round the
shoulder like an epaulette and pulls the arm up, is the scapular
group, things like tidily sorted skeins, thick on the shoulder-blades,
diminished to a tendon string at their insertion in the arm; their
business is to pull the arm back, in opposition to the big pectoral
muscle which pulls it forwards. Here you have your arm working up,
backwards or forwards; but how about pulling it down? An exquisite
little arrangement settles that. Instead of being inserted with the rest
on the outside of the arm-bone, the lowest muscle takes another road,
and is inserted in the under part of the bone, in company with the great
_latissimus dorsi_, and these tightening while the _deltoid_ slackens,
pull the arm down. No other arrangement could have done it with so little
bulk; and an additional muscle on the under-arm or the ribs would have
spoilt the figure of Apollo himself.

Among the paintings of contemporary artists, the one which at that time
afforded Domenico the most unmingled satisfaction was Pollaiolo's tiny
panel of Hercules and the Hydra. There! You might cover it with the palm
of your hand; but in that hand you would be holding the concentrated
strength and valour of the world, the true son of Jove, the most beautiful
muscles that ever were seen! At least the most beautiful save in the
statues of Donatello; for, of course, Donato was the greates