248 ANATOMICAL TECHNOLOGY. 



the lateral wall of the thorax. Sometimes there will be found a 

 slender muscle extending from the muscles covering the ventral 

 surface of the cervical vertebrae to the M. teres which lies along 

 the glenoid border of the scapula. 



General Description. A thick, trapezoidal muscle, from all 

 the ribs and cartilages, excepting the last 3 or 4, to the caudal 

 three fifths of the vertebral border of the scapula. Its cephalic bor- 

 der is continuous with the caudal border of the levator anguli scap- 

 ulas, with which, indeed, it seems to form a single muscle. The 

 independence of the two muscles in man results from the absence of 

 so much of the lev. ang. scap. as in the cat arises from the last 

 three cervical vertebrae. 



Dissection. Near the vertebral end of the first rib note the 

 emergence of an artery and nerve. Extending caudad from this 

 point note the slightly raised border of a long, flat muscle, one of 

 the Scaleni ; divide this at the fourth rib, and reflect the two ends, 

 to the 9th or 10th costal cartilage and to the cervical muscles re- 

 spectively. Nearer the ventrimeson lies another, and wider, ribbon- 

 shaped muscle, the rectus thoracis, the thoracic continuation of the 

 reclus abdominis. Reflect this muscle, together with the strong 

 fascia between it and the ventrimeson, cephalad as far as the 1st 

 rib, and caudad to the 9th or 10th. 



Now turn the arm ventrad so as to expose the ental surface of 

 the combined serratus magnus and levator anguli scapulae. Dis- 

 sect up, or divide, the rather dense fascia which extends from the 

 dorso-caudal and dorso-cephalic borders upon the neck and thorax. 

 Lift the arm from the thorax so as to put the whole muscle upon 

 the stretch, and examine the ectal surface along a line extending 

 from the point of emergence of the artery and nerve above men- 

 tioned corresponding with the vertebral attachment of the first 

 rib to the vertebral border of the scapula at or near the junction 

 of its coracoid and middle thirds, and opposite the vertebral end 

 of the mesoscapula. 



If, along this line, runs the principal branch of the artery, the 

 division of the entire mass into a caudal part, the serratus magnus, 

 and a cephalic part, the leoator anguli scapulae, can usually be 

 made without cutting many fibers ; but in some cases it may be bet- 

 ter to leave the muscles connected. Note, in either case, that the 

 M. serratus presents, in its thoracic half, divisions corresponding to 

 the ribs, while the other muscle is continuous. 



