M. SEREATUS MAGNUS. 249 



Divide the connective tissue, sometimes quite firm, which unites 

 these subdivisions, and then transect tlie muscle itself along a curved 

 line about 3 cm. from the scapula. For greater ease of examining 

 the attachments of the subdivisions, continue the interval just cau- 

 dad of the 4th rib to the cut edge of the muscle. In reflecting the 

 two parts thus formed, note the passage of nerves and vessels to 

 them from the intercostal spaces. The muscle is usually tender, 

 and the tracer should be used rather than the knife in clearing 

 away the connective tissue at the attachments of the subdivisions. 



§ 665. Origin. — A line drawn through all the origins describes 

 about the lifth of a circle, extending from the middle of the 1st rib 

 to the middle of the 9th or 10th. The 4th subdivision extends almost 

 directly dorsad, the first and last extend dorso-caudad and dorso- 

 cephalad respectively, while the intermediate ones vary in direction 

 according to position. 



The first subdivision arises from the 1st rib along nearly or quite 

 the whole of its caudal border ; toward the sternal end it is over- 

 lapped to sohie extent by the attachment of the scalenus above 

 mentioned ; the 2d, from the 2d costal cartilage 1-2 mm. from its 

 union witli the rib, and sometimes by a short tendon ; the 3d and 

 4th, from similar points upon their respective ribs or just at the 

 point of union of the ribs and cartilages ; the 5th, at the point of 

 junction ; the 6th, 7th and 8th, from their respective ribs, at grad- 

 ually increasing distances from their junctions ; the 9th, at about 

 2 cm. from the junction. The lines of attachment of the first and 

 the last coincide very nearly with the axis of the ribs ; those of the 

 next four are nearly at right angles, while those of the remaining 

 three are oblique. A 10th subdivision, from the 10th rib, some- 

 times occurs. It should be carefully looked for. 



Insertion. — The scapular attachment is continuous, but in two 

 parts : (A) the caudal two to three fifths is by a short tendon along 

 the ental edge of the vertebral border of the scapula ; (B) the 

 remainder is by fleshy fibers upon a triangular area near the ver- 

 tebral border of the subscapular fossa, 10-15 mm. long and 4-8 mm. 

 wide. The wider end of this attachment is opposite the vertebral 

 end of the mesoscapula, and is continuous with the insertion of the 

 levator anguli scapul(B. 



