4:1 i Mr. F. O. Ward's P/ij/siological Reinarlcs 



compared to that portion of the |)ectoral which is superior and 

 smaller, and arises from the clavicle; and the latissimus dorsi 

 which is inferior and larger and arises from the vertebrs and 

 ribs, resembles that portion of the pectoralis major which 

 is inferior and larger, and arises from the sternum and ribs. 

 The tendons of the two dorsal, like those of the two pectoral 

 muscles, are continuous at their lower margins, and, as if to 

 render the analogy complete, (though, in fact, to render the 

 leverage suitable,) the lowest fibres of the latissimus dorsi are 

 folded around the teres major, and inserted above it into the 

 humerus; because they are most nearly at right angles with 

 the bone when lifted to strike, and therefore most effective in 

 drawing it down. Fig. 5 is a front view of the insertion of 

 these two muscles, B representing the teres major, C the 

 latissimus dorsi folding round it to gain a higher point of at- 

 tachment, A the tendon of the pectoralis major raised out 

 of its natural position, and D the bicipital groove to the 

 borders of which these muscles are attached. The proposed 

 explanation is further borne out by the comparative anatomy 

 of the pectoral muscle in birds, in which it is developed to 

 a very large size on account of being the principal motor ol 

 the wing. In these animals there is no crossing of the fibres 

 of the pectoralis; they all assist in performing one action, and 

 are consequently inserted in regular order, those which are 

 superior at their origin having also a superior insertion, and 

 vice versa, as may be seen in fig. 6, which is a sketch of the 

 pectoral muscle of a pigeon. The turning under of the fibres 

 represented at a seems at first sight to indicate a decussation 

 of the upper and lower portions of this muscle, similar to that 

 which occurs in the corresponding organ of man. But the 

 resemblance disappears when the muscle is divided along the 

 dotted line h c, and the humeral portion reflected as in fig. 7. 

 It then becomes evident that the lower fasciculi though form- 

 ing a little bundle partly distinguishable from the rest of the 

 muscle, and inserted by a separate slip of tendon, nevertheless 

 join the bone beloxv the upper fasciculi, and below the central 

 point of the whole insertion. Professor Rymer Jones, who 

 very kindly examined with me the muscles of the breast in 

 the pigeon, confirms the accuracy of this observation. 



There is, however, an action, which, as it furnishes man 

 with his most obvious means of self-protection, must have 

 been carefully provided for by Nature, and which seems to 

 throw doubt on the correctness of the foregoing explanation. 

 I mean the action of throwing the extremity forward, as in 

 boxing. In this action, which requires great velocity, although 

 all the fibres of the pectoralis major are in some measure 



