PEONATOR EADII TEEES. 209 



than the anterior, is intimately connected with the strong septa between 

 the several superficial muscles, and seuds off transversely a thin mem- 

 brane to separate the superficial from the deeper group of muscle?. 

 Approaching the back of the "wrist, the transverse fibres increase in 

 number and strength, and these, being stretched somewhat obliquely from 

 the outer margin of the radius on one side to the cuneiform and pisiform 

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

 lujament of the carpus. This structure is attached not only to the 

 points now indicated, but is likewise connected to the several longitu- 

 dinal ridges on the posterior surface of the radius, and thus converts 

 the intermediate grooves into fibro-osseous canals to 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 sjiace 

 corresponds with tlie groove on the outer side of the radius, and gives 

 passage to the extensores ossis metacarpi and primi internodii pollicis, 

 the next three, placed ou the back of the radius, give passage respectively 

 to the two radial carpal extensors, the extensor secundi internodii 

 pollicis, and the conunon extensor of the fingers, with the extensor 

 indicis accompanying it ; between the radius and ulna is the compart- 

 ment i'or the extensor minimi digiti ; and resting in the groove ou the 

 back of the ulna is that for the extensor carpi ulnaris. 



PEONATOR AND FLEXOR MUSCLES. 



The eight muscles on the front and inner part of the fore arm are 

 disposed in two sets, five being superficial, the others more deeply 

 seated. 



The SUPERFICL\L LAYER of muscles comprehends the pronator radii 

 teres, flexor carpi radialis, palmaris longus, flexor carpi ulnaris, and flexor 

 digitorum sublimis. These five muscles are intimately united at their 

 origin from the inner condyle, to which they are attached 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 distinct heads ; one, large and superficial, is derived from 

 the upper part of the inner condylar eminence of the humerus, and from 

 the common tendon above mentioned ; also from the fascia and the 

 inter-muscular septum of the forearm. The second head, a thin fasci- 

 culus deeply placed, comes from the inner margin of the coronoid pro- 

 cess, 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 sui-face at the 

 middle of the outer side of that bone. 



Helations. — The pronator teres is placed superficially in. the greater part of 

 its extent ; but towards its insertion it is crossed by the radial artery and nerve, 

 and the supinator longus muscle. Tlie ulnar border is in contact with the 

 flexor caiiDi radialis and jialmaris longus : the radial border foiins the inner 

 boundary of the angular space at the bend of the aitn, in which are placed the 

 brachial artery, the median nerve, and the tendon of the biceps muscle. Tlie 

 pronator teres covers the flexor sublimis digitorum ; the ulnar artery passes 

 behind the whole muscle, and the median nerve between its two heads. 



Varicth'S. — The coronoid head is sometimes absent. In other cases the muscle 



is prolonged further than usual by a slip rising from tlie intennuscular septum 



above the inner condylar eminence of the humerus, or from the sujiracondylar 



process wlien that is present. This peculiarity is sometimes associated with a 



VOL. I. p 



