314 THE MUSCLES. 



the head of the humeius. In our opinion, this tendon does not belong to the pectoral 

 region, but to that of the shoulder ; and with J. F. Meckel we are inclined to consider it 

 as the coi aco-humeralis, which has followed the coracoid process in its development. 1 



3. The Diaphragm. " In birds, the diaphragm is so differently disposed from what 

 it is in the higher vertebrata, that its existence has been successively described and mis- 

 understood, admitted and refuted, and is still looked upon as problematical by a large 

 number of anatomists. Nevertheless, this muscle exists, and its development is in. 

 perfect harmony with the importance of its functions. It is composed of two planes, 

 which at their origin are confounded with each other, but soon become separated and 

 pursue, one a transverse, the other an oblique direction. The transverse plane is 

 triangular in form, and is carried horizontally from the right to the left ribs against the 

 inferior surface of the lungs. The oblique plane is convex in front, concave behind, and 

 extends from the dorsal aspect of the spine to the sternum, dividing the cavity of the 

 trunk into two secondary cavities the thorax and abdomen. 



" In birds, as in mammals, the diaphragm is therefore intended to perform two principal 

 functions; but to do this perfectly in the former, it is doubled. So far, then, from this 

 inspiratory muscle being absent in birds, or from its existing in a rudimentary degree, 

 they are really provided with two diaphragms: 1, A pulmonary diaphragm, which 

 presides in the dilatation of the lungs ; 2, A thoracic abdominal diaphragm, which par- 

 titions the great cavity of the trunk, and concurs in the inspiration of the air by dilating 

 the large serial reservoirs lying at its posterior suriace. Of these two muscular planes, 

 the first is analogous to that portion of the diaphragm which, in Man and the mammalia, 

 is inserted into the sternum and the ribs ; the second manifestly represents the pillars 

 of the diaphragm." 



This description, taken from the work of M. Sappey, an observer who is as conscien- 

 tious as he is talented, gives a perfectly exact idea of this muscle. 



1 E. Geoffrey Saint-Hilaire, in his memoir on the bones of the sternum (* Philosophic 

 Anatomique,' vol. i. p. 89), in comparing the pectoral muscles of fish to those of birds, 

 also employs the nomenclature of Vicq-d'Azyr, and recognises three pectorals as well. 

 We are, however, obliged to confess ourselves as in opposition to the great master who 

 has established rules to follow in the classification of organs, in consequence of his 

 having limited his comparisons to the two classes of vertebrata he had principally in 

 view. If he had extended his observations to the mammalia, and, in them sought for the 

 analogue of the pectoralis parvus, he would have discovered it, as we have done, in the 

 region of the shoulder, and not in that of the sternum. 



