Ill) AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



which result from the method of attachment of the ligaments. The follow- 

 ing kinds of movement are possible : (a) angular, in which the angle formed 

 by the longitudinal axis of two bones changes, as in flexion and extension or 

 abduction and adduction ; (b) circumduction, in which the longitudinal axis 

 of a bone describes the sides of a cone, the apex of which is in the joint ; 

 (c) rotation, in which ;i bone moves about its longitudinal axis ; (d) gliding, 

 in which a bone so moves as to change its position with reference to its 

 neighbor, without rotation or change of angle. As a matter of fact, most of 

 the movements that are made are the resultant of two or of all of these simple 

 motions. In the gliding joints, in which the articular surfaces are nearly 

 flat (as in the case of the joints between the articular processes of the verte- 

 bra?, and the carpal and tarsal joints), a sliding movement may occur in various 

 directions, and a rotation movement is possible ; but the extent of these 

 movements is very slight, being limited by the strong capsule and ligaments. 

 Singe joints have but a single axis of motion, because the convex and some- 

 what cylindrical surface of one bone fits quite closely the concave surface of 

 the other, and because of tense lateral ligaments which permit of movements 

 in only a single plane. The joint between the humerus and the ulna at the 

 elbow is an example. In this case only flexion and extension are possible, 

 although a slight obliquity of the surfaces causes the head to move in flexion 

 toward the middle line of the body, which is interpreted by some as a screw 

 movement. In this joint the limits of motion arc determined by the contact 

 of the coronoid and olecranon processes of the ulna with the bone in the cor- 

 responding fossa? of the humerus, as well as by the resistance of capsule and 

 ligaments. The knee-joint l is a less simple form of hinge joint. The pres- 

 ence of the semilunar cartilages and the shape of the joint-surfaces cause 

 flexion to be produced by the combined action of sliding, rolling, and rotation 

 movements. In complete extension the lateral ligaments and the posterior 

 and anterior crucial ligaments are put on the stretch, and there is a locking 

 of the joint, no rotation being possible ; in complete flexion, on the other 

 hand, the posterior crucial ligament is tight, but the others are sufficiently 

 loose to allow of a considerable amount of pronation and supination. In the 

 condyloid joint the articulating surfaces are spheroidal, as in the case of the 

 metacarpo- and metatarso-phalangeal joints. These exhibit all forms of 

 angular movement and circumduction. In the saddle-joint there is a double 

 axis of motion — e. g., the articulation of the trapezium with the first meta- 

 carpal bone of the thumb permits of movement aboul an axis extending from 

 before backward, and another, at nearly right angles to this, extending from 

 side to side. All modes of angular movement are possible with such a joint. 

 The ball-and-socket joint, of which the shoulder- and hip-joints are exam- 

 ples, permits of the greatest variety of movements, any diameter of the head 



1 W. Braunne and Fischer have studied with mathematical accuracy the construction and 

 movements of many of the joints of the human body. Their articles are published in the 

 Abhancttungen dor math.-phys. Classe der konigl. Siichsischer Geselhchaft der Wissenschaften, Bd. 

 xvii. and others. 



