3S8 A MANUAL OF ANATOMY 



Posterior Interosseous Nerve. — This is the other and larger 

 terminal branch of the musculo -spiral, its fibres being derived from 

 the sixth, seventh, and sometimes the eighth, cervical. After a 

 short downward course under cover of the brachio-radialis, it 

 winds round the outer side of the radius, passing through the 

 supinator radii brevis. Having reached the back of the limb near 

 the lower border of that muscle, it descends, in company with the 

 posterior interosseous artery, between the superficial and deep groups 

 of muscles. At the upper border of the extensor longus pollicis it 

 leaves the artery and passes beneath that muscle, where it meets 

 the posterior branch of the anterior interosseous artery on the back 

 of the interosseous membrane. Thereafter it passes through the 

 groove on the back of the radius for the extensor communis digi- 

 torum and extensor indicis, lying beneath the tendons and the 

 posterior annular ligament. It terminates on the back of the wrist 

 in a gangliform enlargement, from which branches are given off 

 to the wrist- joint and carpal articulations. 



Branches. — ^The branches are muscular and articular. 



Muscular Branches. — Before piercing the supinator radii brevis 

 the nerve gives branches to that muscle and to the extensor carpi 

 radialis brevior. After reaching the back of the forearm, it supplies 

 the extensor communis digitorum, extensor minimi digiti, extensor 

 carpi ulnaris, the three extensors of the thumb, and the extensor 

 indicis. 



Articular Branches. — ^These irise from the terminal gangliform' 

 enlargement, and are distributed to the wrist- joint and carpal 

 articulations. 



Ulnar Artery. — ^The ulnar artery is the larger of the two termini 

 branches of the brachial, and it arises in the anticubital space 

 opposite the upper part of the neck of the radius. Its destinatioi 

 is the palm, which it reaches by passing over the anterior annulai^ 

 ligament, and there it forms the superficial palmar arch. It ig 

 at first directed downwards and inwards beneath both heads ol 

 the pronator radii teres, flexor carpi radialis, palmaris longusJ 

 and flexor sublimis digitorum, and it here describes a slight curve^ 

 the convexity of which is directed inwards. Having gained th^ 

 front of the ulna it meets the ulnar nerve a little above the centre 

 of the forearm, and it then descends on the outer side of the nerve 

 both structures resting on the flexor profundus digitorum, anc 

 being overlapped by the flexor car^n ulnaris. A little above th^ 

 wrist the artery lies superficially on the outer side of the tendo^ 

 of that muscle. It then crosses over the anterior annular ligament 

 lying close to the outer side of the pisiform bone, with the inter 

 vention of the ulnar nerve, and shortly thereafter it turns outwarc" 

 in the palm towards the thenar muscles. The vessel is divide 

 into three parts — first, second, and third. 



First Part. — This part extends from the origin to the upinr 

 border of the anterior annular ligament. On account of the curve 

 of the vessel at first no definite line can be given to indicate its* 



