MUSCLES OF THE FORE ARM. 425 



different individuals, and run obliquely forwards, some to ter- 

 minate in the flexor profundus tendons, and others in those of 

 the flexor sublimis ; they are called Vincula Accessoria, and 

 are covered by a reflection of the'synovial sheath. 



8. The Pronator Quadratics, 



Is just above the carpal surfaces of the radius and ulna, and 

 between the other muscles and the bone. In the adult it is 

 about two inches wide, and its fibres run across the fore arm. 

 It arises, fleshy and tendinous, from the ridge at the inner sur- 

 face of the ulna, near its lower extremity, and from the front 

 of the bone. 



It is inserted into the corresponding front surface of the ra- 

 dius. 



It rotates the radius inwards.* 



Of the Muscles on the back of the Fore Arm. 



These muscles are ten in number. They arise, for the most 

 part, from the external condyle, and the ridge leading to it, and 

 are extensors either of the fore arm, or of the fingers and thumb. 

 Their origins are less blended with each other than those of the 

 flexor muscles; nevertheless, between several of them there are 

 inter-muscular ligaments which connect them. They are su- 

 perficial and deep-seated. 



1. The Supinator Radii Longus, 



Is situated along the radial edge of the fore arm, immediate- 

 ly beneath the integuments. It arises, fleshy and tendinous, 

 from the higher part of the ridge leading to the external can- 

 dyle; commencing just below the insertion of the deltoid mus- 

 cle, and being here placed between the brachialis internus and 

 the outer head of the triceps. It forms a thick fleshy belly, 

 constituting the external margin of the arm, about the elbow 



* Varieties. This muscle in some very rare cases does not exist. Sometimes 

 it consists in two layers whose fibres cross each other. In a case noticed in the 

 Pennsylvania Hospital by Dr. J. R. Barton, it consisted in two triangular pieecs, 

 the bases of which were reversed. 



36* 



