OF THE RADIUS WITH THE ILXA 



281 



downwards and outwards to be attached to the posterior edge of the lower end of 

 the bicipital tuberosity of the radius and the vertical ridge running from it to the 

 inner border of the bone. Some of its fibres blend with the fibres of insertion 

 of the biceps tendon; behind, it is in close contact with the supiiiator brevi^ ; 

 below, a thin membrane passes off from it to the upper edge of the interosseous 

 membrane; the posterior interosseous vessels pass in the space between it and 

 the interosseous membrane; occasionally a slip is continued into the orbicular liga- 

 ment of the superior radio-ulnar articulation (see fig. 230 A). 



The interosseous membrane (fig. 228) is attached to the ulna at the lowest 

 part of the ridge in front of the depression for the supinator brevis, and along the 

 whole length of the interosseous border as far as the inferior radio-ulnar articulation, 

 approaching the front of the bone in the lower part of its attachment. To the 

 radius it is attached along the interosseous border, from an inch (2 '5 cm. j below 

 the bicipital tuberosity to the sigmoid notch for the lower end of the ulna. It is 

 strongest and broadest in the centre, where the fibres are dense and closely packed; 

 it is also well marked beneath the pronator quadratus, and thickens considerably at 

 the lower end, forming a strong band of union between the two bones. Its fibres 

 pass chiefly downwards and inwards, from the radius to the ulna, though some 



Fio. 230 A. — Upper Poktions of Left Ulna and Radius with Oblique and Orbicular 

 Ligaments : to Show an Occasional Slip from the Oblique Ligament to the 

 Lower Fart of the Orbicular Ligament. This condition is present in the spider monkey 

 (Ateles), which has no external thumb but only rudimentary bones of one. 



(From a dissection by Mr. W. Pearson, Royal College of Surgeons, England.) 



Orbicular ligament 



Occasional slip from oblique liga- 

 ment to orbicular ligament 





Oblique ligament 



take the opposite direction; at the lower end some are transverse. On the posterior 

 surface are one or two bands, which pass downwards and outwards from the ulna 

 to the radius, and frequently there is a strong 1)undle as large as the oblique liga- 

 ment; this, which should be called the inferior oblique ligament (fig. 234), 

 stretches from the ulna, an inch and a half above its lower extremity, downwards 

 and outwards to the ridge above and behind the sigmoid notch of the radius. 



At its attachment to the bones, the interosseous membrane blends with the 

 periosteum. Its upper border is connected with the oblique ligament l)y a thin 

 mem1)rane, Avhich is pierced by the posterior interosseous vessels; and the lower 

 border, which stretches across between the two bones just above the inferior radio- 

 ulnar articulation, assists in completing the caj^sule of that joint. Its anterior 

 surface is in relation with the flexor profun(bi>< digitoram and flexor lougtis pollieis 

 in the upper three-quarters, the lower fourth being in relation with the pronator 

 quadratus. The anterior interosseous vessels and nerve descend along the middle of 

 the membrane, the artery being Ijound down to it. About an inch from the lower 

 end, it is pierced by the anterior interosseous artery. The posterior surface is in 

 relation with the supinator brevis, extensor oss'is metacarpi, extensor primi, extensor 

 secundi internodii pollieis, and the extensor indicis ; at its lower part, also with the 

 posterior branch of the anterior interosseous artery. 



