268 THE ARTICULATIONS. 



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 the 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. Articulations of the metatarsal bones with 

 each other. VIII. The metatarso-phalangeal articulations. IX. The articu- 

 lations of the phalanges. 



I. Hip-joint (Fig. 179). 



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 ligamen- 

 tum 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, being deficient below, where there is a circular depression, which is occu- 

 pied 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 

 to the edge of the obturator foramen. Its lower circumference surrounds the neck 

 of the femur, being attached, in front, to the spiral or anterior intertrochanteric 

 line ; above, to the base of the neck ; behind, to the neck of the bone, about half 

 an inch above the posterior intertrochanteric line. From this insertion the fibres 

 are reflected upward over the neck of the femur, forming a sort of tubular sheath 

 (the cervical reflection), which blends with the periosteum and can be traced as far 

 as the articular cartilage. On the surface of the neck of the femur some of these 

 reflected fibres are raised into longitudinal folds, termed retinacula. It is much 

 thicker at the upper and fore part of the joint, where the greatest amount of 



