THE UPPER LIMB 405 



are chiefly connected by the triangular flbro-cartilage, which is a 

 strong plate. It is attached by its base to the ridge on the radius 

 which separates the sigmoid cavity from the carpal articular surface, 

 and by its apex to the pit on the lower end of the ulna at the root 

 of the styloid process. It is thicker at the circumference than at the 

 centre, and its anterior and posterior borders are connected with the 

 anterior and posterior ligaments of the wrist- joint. Its upper 

 surface is related to the lower end of the ulna, and its lower surface 

 enters into the wrist- joint, articulating with the semilunar bone 

 when the hand is in line with the forearm, and with the faceted 

 part of the upper surface of the cuneiform bone when the hand is 

 adducted. It sometimes presents a perforation. 



The synovial membrane is very loose, and is known as the mem- 

 brana sacciformis. It consists of two parts, vertical and hori- 

 zontal, which are continuous with each other. The vertical part 

 extends upwards between the head of the ulna and the sigmoid cavaty 

 of the radius, and the horizontal part lies between the lower end of 

 the ulna and the upper surface of the triangular fibro-cartilage. 

 When the fibro-cartilage is perforated the membrana sacciformis 

 is continuous with the radio-carpal synovial membrane. 



Arterial Supply. — ^The anterior and posterior ulnar carpal arteries. 



Nerve-supply. — The anterior and posterior interosseous nerves. 



Intermediate Connection between the Radius and Ulna. — This is 

 a variety of syndesmosis. The shafts of the two bones are connected 

 by two ligaments, namely, the interosseous membrane and the 

 oblique ligament. 



The interosseous membrane is a strong expansion which ex- 

 tends between the interosseous borders of the shafts of the radius 

 and ulna. Its fibres pass principally downwards and outwards 

 from the radius to the ulna, but some pass in the opposite direction. 

 Superiorly it reaches to a point about i inch below the bicipital 

 tuberosity of the radius, and inferiorly to the upper part of the 

 sigmoid cavity of that bone. The posterior interosseous artery 

 passes backwards between the two bones over its upper border, and 

 the posterior branch of the anterior interosseous artery pierces it a 

 little above its lower end. The membrane, besides connecting the 

 shafts of the two bones, serves to give origin to muscles of the front 

 and back of the forearm. 



Relations — Anterior. — ^The flexor profundus digitorum and flexor 



longus poUicis, with the anterior interosseous vessels and nerve 



lying between the two, as low as the lower fourth, where the pronator 



I quadratus forms the anterior relation. Posterior. — From above down- 



i wards, the supinator radii brevis, extensor ossis metacarpi pollicis, 



1 extensor brevis pollicis, extensor longus pollicis, extensor indicis, 



1 and, for a short distance below, the posterior interosseous nerve and 



posterior branch of the anterior interosseous artery. 



The oblique ligament is a narrow band which extends from the 

 j tuberosity of the ulna to the radius, close below the lower and back 

 j part of the bicipital tuberosity. Its fibres are directed downwards 



