238 ANATOMICAL TECHNOLOGY. 



to the neighboring muscles, so that its isolation is not always easy. 

 Sometimes it is absent altogether. 



Dissection. The distal part of the cephalic border has been 

 indicated as united with the caudal border of the cephalic division. 

 It is here 1.5-3 mm. wide, but widens gradually as it crosses the 

 axilla and nears the meson. 



At 3-5 cm. from the meson, it leaves the border of the cephalic 

 division, and becomes attached with equal closeness to the caudal 

 border of the ental lamina of the ectopectoralis, which it accompa- 

 nies, until it reaches the meson at the 3d mesosterneber, about the 

 middle of the length of the sternum, exclusive of the xiphisternum. 



648. Origin. By very short tendinous fibers, from the meson 

 of the 3d or 4th mesosterneber, just caudad of the origin of the ental 

 layer of the ectopectoralis. Sometimes the origin on one side is 

 just caudad of that on the other. At the meson its width is 10-15 

 mm.; but it narrows greatly toward the distal end. The caudal 

 border of the distal end is connected with the epitroclilearis. 



M. ECTOPECTORALIS. 



649. Synonymy. The human pectoralis major, G., A, 399 ; Q., A, II, 193 ; " large 

 pectoral," S.-D., A, I, 343. 



Exposure. By the reflection of the MM. claw-deltoideus and pecto-antebrachialis. 



LAMINA ECTALIS, 



Synonymy. " Le premier chef du large pectoral" S.-D., A, I, 343 ; pectoralis, part #, 

 (in part), Miv., B, 146. 



Figures. Part of ectal aspect (72, right side) ; ental aspect of humeral end (72, left 

 side) ; insertion line (68, 69). . 



General Description. Wide, tseniate, from the dorsimeson,' at 

 and cephalad of the pr&sternum, to the middle third of the ventral 

 border of the Tiumerus. 



Dissection. The caudal border extends almost directly laterad 

 from the presterno-mesosternal node, where its mesal end underlies 

 the mesal end of the caudal border of the cephalic division of the 

 M. pecto-antebrachialis. Lift it with great care at about the middle. 



The cephalic border lies nearly parallel with the caudal, at a 

 distance of 2-3 cm., and extends almost directly laterad from the 

 point where the caudal end of the sterno-mastoideus (Fig. 72) passes 

 entad of the pectoral mass. In well-injected specimens this border 

 is indicated, at about the middle of its length, by the disappear- 

 ance, entad of it, of an artery which has emerged from the thorax 

 and curved over the cephalic border of the pectoral mass. 



