MUSCLES OF THE FORE-ARM. 



3C9 



of the triceps extensor cubiti : the fibres of each 

 are perfectly continuous, and there is no line 

 of demarcation between them. An artificial 

 boundary may be made by drawing a line 

 horizontally inwards when the fore-arm is ex- 

 tended on the upper arm, between the outer 

 condyle of the os humeri and the olecranon 

 process of the ulna. With this view of the limit 

 of the upper edge of the anconeus, it may be 

 described as a triangular muscle, the base above 

 and the apex below. This muscle arises ten- 

 dinous from the back part of the outer condyle, 

 its external and anterior edge continuing ten- 

 dinous almost to its insertion; its superior 

 fleshy fibres pass transversely inwards and 

 backwards, to be inserted into the fascia of the 

 fore-arm and also into the olecranon ; the middle 

 and inferior fibres pass backwards to the ulna 

 with various degrees of obliquity, and occupy 

 by their insertion about one-third of the bone 

 from its superior extremity. 



Tliis muscle is a simple extensor of the 

 fore-arm. 



2. Eitentor carpi ulnaris, (ulnaris exter- 

 nus, Scemm.; cubito sus-metacarpien, Chauss.) 

 arises from the back part of the outer con- 

 dylt: Ixjtween the anccneus and the extensor 

 communis digitorum, with which latter muscle 

 it is so intimately connected that, more strictly 

 speaking, it ought to be said to arise in a 

 common tendon. Connected by a narrow 

 origin to the humerus it gradually expands, 

 and about the middle of the fore-arm, a tendon 

 being formed in the centre, it exhibits in its 

 further course a well-marked specimen of the 

 double penniform muscle. The tendon of this 

 muscle, in its passage towards the wrist-joint, 

 runs in an especial groove appropriated for its 

 reception in the back part of the ulna ; it ter- 

 minates by being inserted in the metacarpal 

 bone supporting the little finger. The extensor 

 carpi ulnaris is more or less connected with the 

 fascia throughout the whole of the upper arm. 



This muscle extends the first row of carpal 

 bones on the second and the whole hand on 

 the fore-arm ; it is likewise an adductor of the 

 hand. 



3. Extensor communis digitorum (epicoadylo 

 tas-phalungettien comtnun, Chauss. l)umas) 

 arises from the back part of the outer condyle 

 in common with the extensor carpi ulnaris on 

 its outer side, and the extensor carpi radialis 

 brevior on its inner side. The connexion of 

 this muscle to the os humeri is extremely 

 narrow in comparison with the width of the 

 muscle in the centre of the fore-arm. In its 

 ample attachment to the fascia it resembles the 

 flexor ulnaris, and, like it, is a penniform 

 muscle. We not unfrequenly find a portion 

 of this muscle so entirely distinct from the 

 rest that anatomists have occasionally described 

 it as a separate muscle, under the name of the 

 extensor proprius minimi digiti ; for being 

 inserted into the little finger, it possesses the 

 power of extending that portion of the hand. 

 It passes behind the posterior annular ligament 

 of the wrist-joint, splits into four tendons, 

 which, expanding on the back part of the 

 phalanges of the four fingers, convey the power 



VOL. II. 



of the muscle to each phalanx in an equal 

 degree. The tendons of this muscle in tlirir 

 passage behind the annular ligament of the 

 wrist-joint are clothed by a synovial membrane 

 (reflected like all other synovial membranes) so 

 as to form a perfect' purse or bursa. Ik>th 

 these muscles are intimately connected upon 

 their under surface at the upper part of the 

 arm, with the aponeurosis covering the supi- 

 nator radii brevis. 



This muscle is an extensor of the fingers and 

 the hand on the fore-arm. 



4. Extensor carpi radial'a brevior, (radialit 

 eiternut brevior, Scemm. Epicondylo tut- 

 niftacurpicn, Chauss. Dumas), with a small 

 portion of the extensor carpi radialis lonjrior, 

 occupies the radial division of the poste- 

 rior superficial antibrachial region. This 

 muscle arises from the outer condyle by a 

 flattened narrow origin, in common with the 

 extensor communis digitorum, being overlap|>ed 

 on its outer side by the extensor carpi radialis 

 longior. This muscle, like most we have 

 described in the fore-arm, swells out towards 

 the centre, where, gradually becoming tendi- 

 nous, it again diminishes in size. It passes the 

 same groove in the radius as the extensor carpi 

 radialis longior, and terminates by an insertion 

 into the melacarpal bone of the middle finger. 

 The under surface of this muscle is tendinous 

 at the upper part of the arm, which permits it 

 to play without friction upon the smooth and 

 tendinous face of the supinator radii brevis 

 with which it is in contact. 



Tliis muscle acts as an extensor of the hand 

 on the fore-arm and an abductor. 



b. Deep muiclet of the posterior antibntchial 

 region The muscles in this region com- 

 mencing above, are the supinator radii brevit, 

 the ejctcntor o$$it metacarpi pollicis, the, exten- 

 sor primi inlernodii pollici*, the extensor 

 secundi intemodii, and the indicator. 



1. Supinator radii brevis, (eptcondj/lu-radial, 

 Chauss.) arises tendinous from that portion of 

 the outer and back part of the ulna, unoccupied 

 by the insertion of the anconeus; it arises also 

 from the back part of the outer condyle, covered 

 at its origin from the outer condyle by the 

 extensor communis digitorum and by the exten- 

 sor carpi radialis brevior. Its posterior and 

 external surface is tendinous, its internal fleshy, 

 and it embraces so much of the upper extremity 

 of the radius, as to form an imperfect tube. 

 Anteriorly we find it partly overlapping the 

 tubercle of that bone, with the tendon of the 

 biceps which is inserted into it. Between these 

 and the under surface of the muscle is a large 

 and distinct bursa mucosa ; it covers rather 

 more than the upper third of the radius by its 

 insertion, extending as low down as the pro- 

 nator radii teres. 



Tliis muscle is the main agent in effecting 

 the supination of the hand. 



2. Extensor oisis metacarpi pollicis, (ab- 

 ductor longus pollicis inur.ns, Sirmm. culiiti^- 

 mdi liiis-inetiicarpifti, Dumas,) arises from the 

 ulna, interosseous ligament, and the back part of 

 the radius, opposite the insertion of the pronator 

 radii teres, having to its outer side the supi- 



2 n 



