THE MUSCLES. bi | 
muscles round the eyes and the mouth, of those in the cheeks, and of 
those that raise and depress the eyebrows and the nose, &c. The most: 
important muscles of the skull are those attached to the lower jaw, by 
which the food is chewed. The largest of these, called the temporal’ 
muscle, is attached to the flat surface of the temporal and parietal. 
bones, and is assisted by another, called the masseter, 2 Greek word 
meaning ‘the chewer.” The head is kept balanced on the neck by means. 
of strong muscles, the constant exertion of which is necessary to keep 
it erect. The body is kept erect on the legs by a set of muscles attached 
to the thighs and to the bones of the pelvis, which do the double duty of 
moving the legs and of supporting the trunk, as well as of raising it to an 
erect posture on being bent down. 
The arm is raised from the side by a large muscle on the shoulder, 
called the deltoid from its resemblance to the Greek letter delta, a. From 
under it arise two muscles which respectively bend and extend the fore- 
arm. That which bends the fore-arm is called the biceps! or two-headed 
muscle, and that which extends it the triceps? or three-headed muscle. 
The biceps forms a great part of the fleshy mass in front of the arm, and 
the triceps forms the fleshy mass at the back. The turning movements 
of the hand are effected principally by the radius. The turning of the 
palm of the hand downward is called pronation,? while turning it upware : 
is called supination ;* and the muscles by which these movements are. 
performed are called respectively pronators and supinators. The wrist 
and hand are bent upon the fore-arm by three muscles, which have their - 
origin from the inner end of the humerus, and one of which spreads out 
into a fan-like membrane on the palm of the hand. Under this palmar 
membrane lie the flexor muscles of the fingers. The antagonists of these 
flexors are the common extensors of the fingers, a special extensor of © 
the fore-finger, the muscles of the thumb, accumulated in the ball of the 
thumb, which move it in every direction, and several other muscles of” 
less importance. 
The thigh is raised and advanced by means of two muscles, which 
descend in front of the pelvis—one from the lumbar vertebree, and one: 
from the upper expanded surface of the pelvis. The antagonists of 
these, the muscles which draw back the thigh, have their origin on the- 
back and under surface of the pelvis. 
The muscles which bend the knee proceed from the lower border of the 
pelvis and the back of the thigh-bone, and are inserted in the sides of the 
tibia and fibula, a little below the knee. The tendons of these are felt 
behind the knee, and are known as the hamstrings. The extensors of the 4./ecen 
1 From Latin bis, twice, and caput, a head. 
2 Latin tres, three, and caput, a head. 3 From Latin pronus, with the face downward. 
4From Latin supinus, with the face upward, 
