PLATE XV. 



THE SUPERFICIAL DISSECTION OF THE BACK 

 OF THE FOREARM. 



This plate shows a superficial dissection of the muscles on the 

 back of the forearm. The cutaneous nerves are shown in the sketch 

 plan : (a) External cutaneous of the musculo-spiral ; (b) nerve of 

 Wrisberg; (c) posterior branch of external cutaneous ; (d) posterior 

 branches of internal cutaneous ; (e) dorsal branch of the ulnar ; 

 (/) radial ; (g) twigs from the digital branches of the median ; (h) 

 twigs from the palmar digital branches of the ulnar, supplying the 

 lateral aspect of the fingers. The diagram Plate XVII. shows more 

 clearly the nerve-supply to dorsum of hand and fingers. 



Note on the Ancomus. This muscle is usually supposed to 

 be a segmentation of the lower part of the triceps, both on account 

 of its nerve-supply from the musculo-spiral, and also the con- 

 tinuity of the lower fibres of the triceps with it ; but, on the other 

 hand, in some lizards the anconeus is separate from the triceps, 

 forming a portion of the extensor carpi ulnaris, and its nerve (a 

 branch of the musculo-spiral) supplied also the supinator brevis, 

 afterwards joining the posterior interosseous, and helping to supply 

 the extensors of the fingers. In the alligator, the extensor carpi 

 ulnaris is absent, a large anconeus doing its work, having a double 

 nerve-supply, viz. from the musculo-spiral and posterior interosseous; this has been 

 noted by Luschka as occurring in man. It may be concluded, therefore, that this muscle 

 is more allied to the extensor carpi ulnaris than the triceps, and that its nerve originally 

 took a larger share in the supply of the muscles on the extensor aspect of the forearm.' 



It may also be added that the extensor carpi ulnaris arises from the fascia covering 

 the anconeus for a short distance. 



1 The President : Proc. Boy. Acad. Med. in Ireland, 1888. Lancet report. 



