PRONATOR RADII TERES. 



continuous at its upper margin \vith the fascia of the forearm, and receives some 

 fibres from the tendon of the flexor carpi ulnaris : its anterior surface and lower 

 margin are connected with the palmar fascia, and give origin in part to most of the 

 short muscles of the thumb and little finger. This structure may be considered in 

 some measure as a deep thickened portion of the fascia of the wrist. 



The posterior portion of the aponeurosis of the forearm, much thicker than the 

 anterior, is intimately connected with the strong septa between the several super- 

 ficial muscles, and sends off transversely a thin membrane to separate the superficial 

 from the deeper group of muscles. Approaching the back of the wrist, the trans- 

 verse fibres increase in number and strength, and these, being stretched somewhat 

 obliquely from the anterior margin of the radius on one side to the pyramidal and 

 pisiform bones and the palmar fascia on the other, constitute the posterior annular 

 ligament of the carpus. This structure is attached not only to the points now 

 indicated, but is likewise connected to the several longitudinal ridges on the 

 posterior surface of the radius, and thus converts the intermediate grooves into 

 osseo-fibrous canals which lodge the tendons of the extensor muscles. There are six 

 separate spaces so enclosed, and each is lined by a distinct synovial sac. The 

 outermost space corresponds with the groove on the outer side of the radius, and 

 gives passage to the exten sores ossis metacarpi and brevis pollicis ; the next three, 

 placed on the back of the radius, give passage respectively to the two radial carpal 

 extensors, to the extensor longus pollicis, and to the common extensor of the 

 fingers, with the extensor indicis ; between the radius and ulna is the compartment 

 for the extensor minimi digit i ; and corresponding to the groove on the back of the 

 ulna is that for the extensor carpi ulnaris. 



PRONATOR AND FLEXOR MUSCLES. 



The eight muscles on the front and inner part of the forearm are disposed in 

 two sets, five being superficial, the others more deeply seated. 



The SUPERFICIAL GROUP of muscles comprehends the pronator radii teres, flexor 

 carpi radialis, palmaris longus, flexor carpi ulnaris, and flexor sublimis digitoruin. 

 These five muscles are intimately united at their origin from the inner condyle, 

 being attached to this by a common tendon which gives fibres to each, and also 

 sends septa between them. 



The pronator radii teres muscle, the most external of the group, arises by two 

 heads : one, large and superficial, is derived from the upper part of the inner 

 condyle of the humerus, and from the common tendon above mentioned ; also from 

 the fascia and the intermuscular septum on its inner side. The second head, a thin 

 fasciculus deeply placed, comes from the inner margin of the coronoid process, and 

 joins the other at an acute angle. The fleshy belly thus formed proceeds outwards 

 and downwards, and ends in a flat tendon which turns over the radius, and is 

 inserted into a rough impression at the middle of the outer surface of that bone. 



Relations. The pronator teres is placed superficially in the greater part of its extent ; 

 but towards its insertion it is crossed by the radial vessels and nerve, and covered by the 

 gupinator longus muscle. The ulnar border is in contact with the flexor carpi radialis and 

 flexor sublimis digitorum : the radial border forms the inner boundary of the angular space 

 at the bend of the arm, in which are placed the brachial vessels, the median nerve, and the 

 tendon of the biceps muscle. The pronator teres lies over the brachialis anticus and the 

 radial origin of the flexor sublimis digitorum ; the ulnar artery passes behind the whole 

 muscle, and the median nerve between its two heads. 



Varieties. The coronoid head is sometimes absent. In other cases the muscle is pro- 

 longed farther than usual by a slip arising from the intermuscular septum above the inner 

 condyle of the humerus, or from the supracondylar process when that is present. This 



