258 TEE MUSCLES. 



B. Posterior BracMcd Begion. 



This is composed of five muscles, wtich have their movable insertion in 

 common on the summit of the olecranon, and are consequently designated 

 olecranian muscles. With reference to their action, they are also designated 

 extensors of the fore-arm, and are distinguished into long, short, middle, and 

 small. 



Preparation. — The muscles of this region ought to be studied before those of the 

 preceding region. To dissect the large and short extensors, it is necessary to lay the 

 limb on its inner face, remove the slight fibrous layer which covers these two muscles, 

 and raise the abductors of the arm, which in great part conceal their origin. The limb 

 is kept in the same position for the dissection of the small extensor, which is not easily 

 accomplished, as it is almost entirely concealed by the short extensors which, besides, 

 closely adhere to it. To dissect the long and middle extensors, it suffices to turn the 

 limb on its external surface and cut away the vessels, nerves, and lymphatics which 

 partly cover the latter. The first, lying closely to the internal face of the large extensor, 

 requires some care in order to free it from its aponeurosis. 



1. Long Extensor of the Fore-arm. (Fig. 121, 6.) 



Synonyms. — Scapulo-olecranius — Girard. (A portion of the caput magnum of the 

 triceps extensor brachii — Percivall. Long scapulo-olecranius— Leyh.') 



Form — Situation. — This is a wide muscle, flattened within and without, 

 and applied against the inner face of the large extensor, -to which it closely 

 adheres. 



Structure and Attachments. — It is composed of an aponeurosis, attached 

 to the posterior border of the scapula — fixed insertion : and a muscular 

 portion, easily divisible into two fasciculi, one anterior, the other posterior. 

 These two fasciculi are formed of vertical fibres, the longest of which are 

 posterior, and terminate at the posterior border of the ulna, as well as on 

 the antibrachial aponeurosis — movable insertion. 



BekUions. — Outwards, with the large and middle extensors ; inwards, 

 with the sterno-trochineus, the adductor of the arm, and the great dorsal. 

 Its aponeurosis adheres closely to the tendinous portion which terminates 

 the last-named muscle, and its anterior border is united to the aponeurotic 

 sheath of the coraco-radialis by a particular fibrous fascia, which covers the 

 vessels and nerves on the inner aspect of the arm. 



Action. — It extends the fore-arm, and renders the antibrachial aponeurosis 

 tense. 



2. Large Extensor of the Fore-arm. (Figs. 119, 7; 121, 7.) 



%norei;ms.— Scapulo-olecraniua major— CWrartJ. The long portion of the triceps 

 braohialis of Man. (Portion of the caput magnum of the triceps extensor brachii— 

 Percivall.) 



Volume— Form — Situation. — An enormous, short, and triangular muscle, 

 occupying, with the short extensor, the space comprised between the 

 posterior border of the scapula and the humerus. 



Structure and Attachments.~The fleshy mass constituting this muscle is 

 formed of very thick fasciculi, among which are found some aponeurotic 

 bands. These fasciculi have their origin on the dorsal angle and the axillary 

 border of the scapula, either directly, or through the medium of two strong 

 fibrous layers, between which they are at first included. They are afterwards 

 directed backwards and downwards, and converge towards a thick tendon 

 which occupies the posterior and inferior angle of the triangle represented 

 by this muscle. The tendon terminates by attaching itself to the summit of 



