592 | THE NERVOUS SYSTEM. 
POSTERIOR INTEROSSEOUS NERVE. 
The posterior interosseous nerve (r. profundus, n. interosseus antibrachii 
dorsalis) is entirely muscular and articular in its distribution, and it arises like 
the radial beneath the brachio- 
radialis muscle. Directed 
obliquely downwards and 
backwards, it reaches the back 
Triceps (outer head) of the forearm, after passing 
round the outer side of the 
radius, by piercing the fibres 
of the supinator radu brevis 
muscle (Fig. 436). On the back 
ip of the forearm it is placed in 
[}~Triceps (inner head) the upper part of its course be- 
neath the superficial extensor 
muscles, and upon the sup- 
extensor carp\tadialis _ imator xadil, brevis) anligjer 
itiaoe carr dene tensor ossis metacarpi pollicis, 
Drewior (Cres) along with the posterior inter- 
MUSCULO-SPIRAL NERVE, osseous artery. Im the lower 
| half of the forearm it passes 
Se beneath the extensor longus 
Posterior InteRosseous pollicis, and lies upon the 
= a interosseous membrane. At 
the wrist it passes beneath 
the extensor tendons on to 
Extensor ossis metacarpi =the back of the carpus wleme 
‘Triceps (long head) 
Brachio-radialis 
Brachialis anticus 
External condyle 
Insertion of 
triceps 
Extensor muscles 
(origin) 
Supinator radii | 
brevis jf 
| 
Flexor carpi i 
ulnaris | 
Extensor carpi 
ulnaris 
pollicis 3 : . : 
it terminates in a gangliform 
Extensor carpi radialis enlargement of small size, 
longior (tendon) 
Extensor longs neta aia from which branches pass to 
Dye i brevior (tendon) the inter-carpal articulations. 
The posterior interosseous 
nerve supplies the following 
branches :— 
RADIAL NERVE (1) Terminal articular 
Extensor brevis pollicis 
Extensor indicis 
eS BANOO branches to the carpal joints. 
tensor athe Extensor carpi radialis (2) Muscular branches, in 
longior (tendon) 
Extensor ossis metacarpi_ 1ts course through the forearm. 
pollicis PR ic 
Extensor carpi radialis Thus on the outer side of the 
Peet ive pollicis Tadius it supplies the extensor 
digiti (tendon) 
Extensor communis — 
digitorum (tendon) 
Extensor indicis — Extensor longus carpl radialis brevior and the 
pollicis supinator brevis muscle before 
First dorsal inter- 4{ enters the fibres of the last- 
osseous muscle 
named muscle. After emerg- 
ing from the supinator brevis 
it supplies a large bundle of 
nerves whichenter theextensor 
communis digitorum, extensor 
minimi digiti, and extensor 
carpi ulnaris near their origins. 
Lower down the forearm the 
nerve gives off branches to 
the extensor ossis metacarpi 
pollicis, extensor longus and 
extensor brevis pollicis, and — 
Fic. 436.—THE MUSCLES OF THE BACK OF THE FOREARM fe 0 
extensor indicis. 
(the superficial muscles have been reflected). 
