M. ENTOTRICEPS. 263 



M. ECTOTRICEPS. 



684. Synonymy. The external head of the human triceps, G., A, 409, Q., A, 1, 207 ; 

 "triceps externe," S.-D., A II, 347 ; " court extenseur de I'avant bras," Ch., A, 273 ; short 

 extensor of the forearm, Ch. (Fl.), A, 259 ; first division of the triceps, Miv., B, 149. 



Figures. Ectal aspect (66, 67, 74) ; origin area (71). 



Posture. The arm may rest upon the shoulder and wrist, the 

 elbow looking upward, the dorsal aspect of the braehium toward 

 the dissector, and the antebrachium leaning against a block. 



Exposure. The muscle is subcutaneous in its whole length, and 

 was exposed in removing the skin from the cephalic aspect of the 

 brachium. 



General Description. A flattened fusiform mass, from the 

 proximal part of the deltoid ridge of the Jiumerus to the cephalic 

 aspect of the olecranon. 



Dissection. The dorsal border was cut from the cephalic border 

 of the meditriceps, and the whole muscle is attached to the subja- 

 cent muscles only by connective tissue ; an artery enters its ental 

 surface a little proximad of the middle of the length, and must be 

 divided. The ventral border is attached to the brachialis upon the 

 cephalic side of the arm by a strong fascia, but at the middle of the 

 muscle it is thinner than elsewhere, and may be cut first. Then 

 transect the muscle and reflect it, dividing the fascia between its 

 ventral border and the adjacent parts. 



Origin. By a thin tendon from the proximal part of the deltoid 

 ridge and from the dorso-cephalic aspect of the neck of the humerus. 

 The line of attachment is curved so as to pass ventrad of the tuber- 

 cle for the insertion of the micostalis, and dorsad of the origin of 

 the middle division of the entotriceps, some fibers of which seem to 

 spring from the tendon of the ectotriceps. The line begins about 

 o mm. proximad of the proximal end of the line of insertion of the 

 spino-delto ideus. 



Insertion. The proper tendon is 5 mm. wide at its attachment 

 to the cephalic border of the olecranon, but the distal half of the 

 ventral border of the muscle is so firmly connected to the brachial 

 and antebrachial fascia that it may be said to have a general inser- 

 tion upon the region about the elbow. 



M. ENTOTRICEPS. 



685. Remark. The remaining extensors of the antebrachium are not easy to 

 homologize with the parts of the human triceps, anconeus and subanconeus; the names 



