M. PECTO-ANTEBEACHIALIS. 237 



respectively, to the dorsal harder of the antebracJiium near tlie 

 elbow. 



Posture. — Dorsiciimbent, the head toward the dissector ; a block 

 under the shoulders so that the head and neck hang down. 



§ 646. Dv. Cephalica. — ^Dissection. — The ceiDhalic border has 

 been indicated during the dissection of the cla'DO-deltoideus, to 

 which it is attached excepting at tlie ends. Trace it for 2-3 cm. 

 both ways from the middle. Then feel ui^on the meson, about 

 3 cm. from the tip of the prsesternum, for toe elevation corresponding 

 with the first sternal node, or for the attachment thereto of the sec- 

 ond costicartilages. Laterad from that point runs a white line, 

 which marks the caudal margin of the muscle. Toward this line 

 dissect up the muscle from its cephalic border, at about the mid- 

 dle of the length of the latter, and transect. 



In reflecting the mesal xDart of the muscle, note its close attach- 

 ment to the subjacent ectopectoralis, and that it joins its platetrope 

 by a median raphe. The distal part of the muscle is much more 

 easily separable from the subjacent muscle, but, about 1 cm. ven- 

 trad of the level of the antebrachium, its caudal border is joined 

 by the caudal division of the muscle. At this point the muscular 

 fibers of both divisions are replaced by tendinous fibers. 



The tendon thus formed seems to be continuous witli the general 

 antebrachial fascia, but, if this fascia be divided along a line cor- 

 responding with the cephalic border of the muscle, the tendon may- 

 be traced across the caudal surface of the antebrachium and found 

 to terminate upon the dorsal aspect of the ulna. The examination 

 of the details of the insertion may be deferred until after the dissec- 

 tion of the caudal division. 



Origin. — From a median raphe common to it and its platetrope, 

 and extending the whole length of the prsesternum, excepting, 

 sometimes, its caudal or cephalic 1-2 mm. 



Insertion. — By tendinous fibers along the distal third of the 

 oblique caudal border of the subcutaneous surface near the proxi- 

 mal end of the dorsal aspect of the ulna. The cephalic border of the 

 tendon is closely attached for part of its length to the caudal border 

 of the clavo-deltoideus, and its caudal border is continuous with the 

 fibers forming the tendon of the caudal division of the muscle, 



^ 647. Dv. Caudalis. — Posture and Exposure as with the 

 cephalic division. The muscle is very slender and closely attached 



