SERRATFS MAGNUS MUSCLE. 



197 



thus : — «, those from the first and second digitations form a thick 

 bundle which terminates on the flat area in front of the upper angle of 



Fig. 168. — Lateral ViHw 

 OP THE Trunk, show- 

 ing THE Serratus Mag- 

 nus Muscle. (A. T.) | 



a, coracoid process of 

 the scapula ; b, glenoid 

 cavity ; c, lower angle ; 

 <l, first dorsal vertebra ; I, 

 VI, Xn, the first, sixth, 

 and twelfth ribs ; 1 , upper 

 portion of the serratus 

 magnus attached to the 

 first and second ribs ; 2, 

 second or middle portion 

 attached chiefly to the 

 third rib ; S, lower or fan- 

 shaped portion attached to 

 the ribs from the fourth 

 to the ninth ; 4, externtd 

 intercostal muscle ; 5, cos- 

 tal origins of the transver- 

 salis abdominis ; +, sca- 

 pular extremities of the 

 levator scapuiiB and omo- 

 hyoid muscles. 



the scapula ; h, those 

 of the third and fourth 

 digitations, but es- 

 pecially the first of these, ^vhich is the inferior digitatiou of the second 

 rib, spread out into a triangular layer, the thinnest part of the muscle, 

 and are attached along the line in front of the base of the scapula, 

 extending from the place of insertion of the preceding part nearly 

 to the lower angle of the bone ; c, the remaining five or six digita- 

 tions converge in the form of a fan, and terminate posteriorly in a 

 thick mass, which is attached to the flat surface in front of the lower 

 angle of the scapula. 



Relatiom. — By its deep surface, the serratus magTius rests on the upper ribs, 

 the intercostal muscles, and part of the seiTatus posticus superior. Its outer 

 surface is in contact posteriorly with the subscapular and latissimus dorsi 

 muscles, and forms anteriorly the internal wall of the axilla, being subcutaneous 

 in the lower part of its extent. 



Varieties. — Not unfrequently the lowest slip of the muscle extends to the tenth 

 rib : in other instances the number of costal slips is diminished, occasionally by 

 the suppression of the fii-st. but oftener by the absence of some of the lower 

 digitations. so that the muscle does not pass lower than the seventh rib. The 

 muscle has been observed divided into three parts : sometimes the middle part 

 is absent ; and in various instances the serratus has been observed united 

 partially with the levator scaprda;. the external intercostals, or the external 

 oblique. With the levator scapulas it forms one muscle in many mammals. 



Nerves. — The nerves which supply the anterior muscles passing from the 

 trunk to the upper limb are all derived from parts of the brachial plexus. 

 The nerve of the subclavius is a small twig from a loop between the fifth 

 ajid sixth cervical nerves. The large nerve of the serratus magnus, called 

 posterior thoracic, proceeds from the same nerves and pierces the middle scalene 

 muscle. The nerves of the pectoral muscles, named anterior thoracic, are in two 



