NERVI ACCELERANTES 61 



IV. Operation. Place preparation on its left side. Draw right forelimb Obs, 39. 



forward with shoulder and elbow fully extended, and attach a heavy clip- ^^a^'t-^ate and 

 ' f , n. accelerantes 



weight to the paw to keep the limb in position. Attach clip-weights to hind 



feet, drawing them backwards. Feel through the skin the dorsal edge of 



scapula. Make a skin incision (PI. IV, fig. 1), about 7 cm. long, parallel with 



and about 2 cm. to right of the mid-dorsal line ; the front end of the incision 



should be on a level with the front of the head of the humerus ; the posterior 



end should lie on a level with the posterior border of the scapula. At each 



end of this incision make a transverse one extending from mid-dorsal line 



laterally for about 7 cm., and at right angles to the longitudinal incision. 



Reflect the two skin-flaps and retract them with clip-weights. 



The muscles covering scapula lie exposed (PI. IV, fig. 2) ; note the posterior 

 edge of cephalo-humeral, the anterior edge of latissimus dorsi, and the 

 trapezius between them. Cut through this last near the mid-dorsal line, reflect 

 outward the portion covering the supra-scapular fossa, and detach it from the 

 scapular spine. Note the fhomboidei muscles. 



By means of the small curved ' packing-needle ' pass a string deep to the 

 whole mass of the rhomboidei near their insertion into the dorsal edge of 

 scapula. Tie the muscles tightly and cut them between the ligature and 

 the scapula. Retract with clip-weights the ligated muscle towards mid-dorsal 

 line. 



The scapula thus partially freed is now to be displaced (PI. IV, fig. 3) 

 laterally ; this can be done suitably by adducting the right forearm towards 

 the neck and rotating it clockwise as looked at from behind, and then retaining 

 it in this position by a clip- weight to the paw and by a heavy hook- weight 

 fixed to the top of the muscular mass covering dorsal edge of scapula, so pulling 

 the wing of the shoulder laterally (PI. IV, fig. 3). The hook-weight may be 

 hung over a cross-piece in a short standard with heavy base, this giving better 

 leverage for the purpose than the table-edge. The lateral luxation of the 

 shoulder-blade is assisted by somewhat flexing and lifting the truncated neck. 

 This slackens the levator anguli scapulae (PI. IV, fig. 3), which, conjoined 

 posteriorly with serratus magnus, stretches as a thick muscular band backwards 

 and to the right from the lateral processes of the cervical vertebrae in front 

 to the hind end of scapula behind. 



Explore with the finger the deep space lateral to this muscular band, and 

 note the supra-scapular nerve, and, posterior and deep to that, the brachial 

 flexus, and posterior to that again the first rib. Feel with the finger dorsal 

 to levator ang. scap. the rest of the first rib, following it to its articulation 

 at the vertebra. Then make out with the finger the second and third ribs. 

 Reflect laterally the origins of serratus from the second rib, first intercostal 



