400 JAMES CRAWFORD WATT 



tally and deep to that part of the biceps tendon inserted here, 

 and deep to the origin of the muscles of the forearm. 



This portion of the muscle is supplied by the musculocutaneous 

 nerve, which is normal, as this portion of the muscle develops 

 from the ventral musculature of the arm. 



The insertion of the brachialis on the radius is to be expected 

 here, as the ulna is absent, and because it is a frequent abnor- 

 mality to have accessory insertion on the radius in addition to 

 its ulnar insertion. Indeed, in addition to the ulnar insertion 

 in some of the lower animals, such as the horse, the ruminants and 

 the rodents, a radial attachment is normal and in a few species, 

 such as the platypus the radial insertion is the only one found. 



Lateral portion (figs. 7, 9 and 10, Br.) 



This portion is so distinct from the medial portion as to be 

 practically a separate muscle. It is also divided longitudinally 

 into two completely separate bundles. 



Origin. The two bundles of this muscle arises alongside of 

 each other, following the lower half of the circumference of the 

 deltoid tubercle. 



Insertion. They pass down the arm as parallel fasciculi and 

 are inserted on the lateral border of the radius in line with each 

 other, the most lateral fasciculus being at least a third the dis- 

 tance down the shaft of the radius. This portion of the muscle 

 is supplied by the radial nerve and represents the portion of the 

 muscle developed from the dorsal musculature of the arm and 

 has, in this instance, separated from the rest of the muscle 

 formed from the ventral elements. The radial nerve normally 

 supplies a small portion of the human brachialis muscle on the 

 lateral side, thus indicating the normal composition of the muscle, 

 which always has a small portion of the dorsal musculature in- 

 cluded in it. Le Double cites cases where the brachialis muscle 

 has been found divided into two distinct heads, as found in this 

 case, either one of which may be subdivided again. He does not 

 state the nerve supph% but it is probable the primary separation 

 is between the dorsal and ventral elements of the muscle. 



