THE MUSCLES OF THE UPPER EXTREMITY. 73 



well as from a contiguous strip of the anterior surface 

 of the sternal body. It also finds origin from a tendi- 

 nous expansion stretching between the corresponding 

 coracoid and the os furcula, and from the anterior 

 sternal extremity of the lower third of the coracoid 

 itself (Fig. 24). From these several points of origin 

 the muscular fibres of the second pectoral rapidly 

 contract as they converge, to pass upward and round 

 the coracoid to its posterior aspect. As they approach 

 the shoulder-joint the carneous fibres become tendinous 

 to form a rounded and strong cord. This passes through 

 the canal formed by the scapula, coracoid, and clavicle, 

 and immediately upon emerging above it is directed 

 outwards and downwards, to be inserted as a strong and 

 somewhat flattened tendon just anterior to the radial 

 crest of the humerus, on the same side but nearer the 

 humeral head than the pectoralis major. 



It must not be understood from what I have just said 

 that the fibres of this muscle pass directly to their 

 humeral tendon, for more strictly speaking they 

 gradually merge, as they pass in that direction, into a 

 tendinous sheet which traverses the muscle longitudinally, 

 and appears as a tendinous line upon its anterior aspect. 



Through the leverage gained by the tendon of this 

 muscle passing through the osseous canal formed by the 

 bones of the shoulder-girdle, it acts as a levator of the 

 wing, the humerus being raised by its contraction. And 

 this mechanism is very prettily effected in spite of the 

 fact that the chief weight of this muscle is thrown in 

 favour of depressing the centre of gravity of the bird's 

 body, a very essential point to be attained, in fact a 

 positive requirement during flight. 



Owen says, " In the Penguins, Guillemots, and Gulls, 

 this muscle is almost the largest of the three, occupying 



