362 THE ARTICULATIONS. 



sheath surrounding which is connected to each side of the groove. By their deep 

 surface they form part of the articular surface for the head of the metacarpal bone, 

 and are lined by a synovial membrane. 



The Lateral Ligaments are strong, rounded cords placed one on each side of 

 the joint, each being attached by one extremity to the posterior tubercle on the 

 side of the head of the metacarpal bone, and by the other to the contiguous 

 extremity of the phalanx. 



Actions. The movements which occur in these joints are flexion, extension, 

 adduction, abduction, and circumduction ; the lateral movements are very limited. 



Surface Form. The prominences of the knuckles do not correspond to the position of the 

 joints either of the metacarpo-phalangeal or interphalangeal articulations. These prominences 

 are invariably formed by the distal ends of the proximal bone of each joint, and the line indi- 

 cating the position of the joint must be sought considerably in front of the middle of the knuckle. 

 The usual rule for finding these joints is to flex the distal phalanx on the proximal one to a right 

 angle ; the position of the joint is then indicated by an imaginary line drawn along th'e middle of 

 the lateral aspect of the proximal phalanx. 



XI. Articulations of the Phalanges. 

 These are ginglymus joints. The ligaments are 



Anterior. Two Lateral. 



The arrangement of these ligaments is similar to those in the metacarpo- 

 phalangeal articulations ; the extensor tendon supplies the place of a posterior 

 ligament. 



Actions. The only movements permitted in the phalangeal joints are flexion 

 and extension ; these movements are more extensive between the first and second 

 phalanges than between the second and third. The movement of flexion is very 

 considerable, but extension is limited by the anterior and lateral ligaments. 



ARTICULATIONS OF THE LOWER EXTREMITY. 



The articulations of the Lower Extremity comprise the following groups : 

 I. The hip-joint. II. The knee-joint. III. The articulations between the tibia 

 and fibula. IV. The ankle-joint. V. The articulations of the tarsus. VI. The 

 tarso-metatarsal articulations. VII. The rnetatarso-phalangeal articulations. 

 VIII. The articulations of the phalanges. 



I. Hip-joint (Fig. 253). 



This articulation is an enarthrodial or ball-and-socket joint, formed by the 

 reception of the head of the femur into the cup-shaped cavity of the acetabulum. 

 The articulating surfaces are covered with cartilage, that on the head of the femur 

 being thicker at the centre than at the circumference, and covering the entire 

 surface, with the exception of a depression just below its centre for the ligamentum 

 teres ; that covering the acetabulum is much thinner at the centre than at the 

 circumference. It forms an incomplete cartilaginous ring of a horseshoe shape, 

 deficient below and in front, and having in its centre a circular depression, which 

 is occupied in the recent state by a mass of fat covered by synovial membrane. 

 The ligaments of the joints are the 



Capsular. Teres. 



Ilio-femoral. Cotyloid. 



Transverse. 



The Capsular Ligament is a strong, dense, ligamentous capsule, embracing the 

 margin of the acetabulum above and surrounding the neck of the femur below. 

 Its upper circumference is attached to the acetabulum, above and behind, two or 

 three lines external to the cotyloid ligament ; but in front it is attached to the 

 outer margin of this ligament, and opposite to the notch where the margin of this 

 cavity is deficient, it is connected to the transverse ligament, and by a few fibres 



