THE MEDIAN NERVE. 303 



in the form of a branch leaving- the median in common either with the muscular offsets at the 

 elbow or with the anterior interosseous nerve, and passing- with or near the ulnar artery to 

 join the ulnar nerve about the middle of the forearm : less frequently the connection is by 

 means of a loop or small plexus, from which twigs are given off to the flexor profundus 

 digitorum muscle : this communication between the median and ulnar nerves in the upper 

 part of the forearm is normal in most apes (Hepburn, Hofer). and in lower mammals 

 (Bardeleben). A communication in the lower part of the forearm is rare. In two cases a 

 branch was seen passing from the median nerve at the elbow, over the superficial muscles, to 

 join the ulnar (T. J. Jeans). Very seldom a branch runs from the ulnar to the median trunk 

 or to its anterior interosseous branch. The communicating branch between the median and 

 ulnar nerves in the palm is commonly directed from the ulnar to the median, but it may run 

 in the opposite direction, or the communication may be looped or plexiform in arrangement. 

 Absence of the communication has been noted. In two cases described by Klint the anterior 

 interosseous nerve received a branch from the musculo-spiral (posterior interosseous ?) through 

 the interosseous membrane. A communication between the anterior and posterior interosseous 

 nerves at the lower end of the interosseous space is noticed by Martin and Rauber. (F. Curtis, 

 " Recherches anatomiques sur Tanastomose du Median et du Cubital a 1'avant-bras," Intemat. 

 Monatschr. f. Anat. u. Hist., iii, 1886 ; Third Annual Report of Committee of Collective 

 Investigation of the Anat. Soc., by Arthur Thomson, Journ. Anat., xxvii, 1892.) 



The digital nerves in the palm are often pierced by the corresponding arteries. Four cases 

 are recorded by Gruber in which the nerve supplying the adjacent sides of the middle and ring 

 fingers arose from the trunk in the forearm. A branch from the median nerve to the abductor 

 indicis muscle was observed by Brooks. 



SUMMARY. The median nerve gives cutaneous branches to the palm, and to 

 three and a half fingers. It supplies the pronator muscles, the flexors of the carpus 

 and the long flexors of the fingers (except the ulnar flexor of the carpus, and part 

 of the deep flexor of the fingers), likewise the outer set of the short muscles of the 

 thumb, and two lumbricales. Articular filaments are also given to the joints of the 

 elbow, wrist, and fingers. 



A great similarity will be observed in the distribution of the median and ulnar 

 nerves. Neither gives any offset in the arm. Together they supply all the muscles 

 of the front of the forearm and in the hand, and together they supply the skin of 

 the palmar surface of the hand, and impart tactile sensibility to all the fingers. 



Musculo-spiral nerve. The musculo-spiral nerve (n. radialis of French and 

 German writers), the largest offset from the brachial plexus, is derived from the 

 sixth, seventh, and eighth cervical nerves, in some cases also from the fifth. It 

 occupies chiefly the back part of the limb, and supplies nerves to the extensor 

 muscles, as well as to the skin. 



Arising behind the axillary vessels from the posterior cord of the brachial plexus, 

 of which it is the principal continuation and the only branch prolonged into, the 

 arm, it soon turns backwards with the superior profunda artery between the long 

 and internal heads of the triceps, and runs beneath the external head of that muscle, 

 in the hinder part of the spiral groove of the humerus, to the outer side of the arm. 

 It then pierces the external intermuscular septum, and descends in the interval 

 between the supinator longus and brachialis anticus muscles nearly to the level of 

 the outer condyle of the humerus, where it ends by dividing into the radial and 

 posterior interosseous nerves. Of these, the radial is altogether a cutaneous nerve, 

 while the posterior interosseous is the muscular nerve of the back of the forearm. 



The branches of the musculo-spiral nerve may be classified according as they 

 arise on the inner side of the humerus, behind that bone, or on the outer side. 



A. Internal branches. 



(a) Muscular branches for the long and inner heads of the triceps (7, 8 c). That for 

 the inner head gives two or three filaments to the upper part of the muscle, and then 

 descends by the side of the ulnar nerve, to which it is often closely adherent for a 

 part of its course, and enters the lower short fibres of the head. This long filament 

 is named by Krause the ulnar collateral branch. 



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