THE MUSCLES IN BIRDS. 379 



other muscles of the bird put together, is attached to the furculum, to the great 

 ridge of the sternum, and to the last ribs ; it is inserted into the very salient 

 rugged outline of the humerus. It is by this muscle that birds are able to give 

 those powerful strokes of the wings which are necessary in flight." 



The deep or small pectoral is " placed in the angle formed by the body of the 

 sternum and its crest, and in the interval between the furculum and the coracoid 

 bone. Its tendon passes through the foramen formed by the union of the 

 furculum, the coracoid bone, and the scapula, as over a pulley ; it is inserted 

 above the head of the humerus, which it raises. It is by means of this arrange- 

 ment that nature has been able to place an elevator and depressor at the inferior 

 surface of the trunk so far from the centre of gravity, without which the bird 

 would have been liable to lose its equihbrium and tumble over head foremost in 

 the air." ' 



Cuvier, adopting the nomenclature of Vicq-d'Azyr, called this muscle the 

 middle pectoral, and he gave the name of small pectoral to a triangular fasciculus 

 which leaves the lateral angle of the sternum and the base of the coracoid bone, 

 to be inserted under the head of the humerus. 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 curaco-humeralis, which has followed 

 the coracoid process in its development.^ 



3. The Diaphragm. — " In Birds, the diaphragm is so differently disposed 

 from what it is in the higher Yertebrata, that its existence has been successively 

 described and misunderstood, 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 partitions the great cavity of the trunk, 

 and concurs in the inspiration of the air by dilating the large aerial reservoirs 

 lying at its posterior surface. Of these two muscular planes, the first is analogous 

 to that portion of the diaphragm which, in Man and the Mammalia, is inserted 



' Cuvier, Lemons d'Anntomie Compar^e. 



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

 Anatomique, vol. i. p. 89), in comparing the pectoral muscles of Fishes to those of Birds, also 

 employs the nomenclature of Vicq-d'Azyr, and recognizes three pectorals as well. We are, 

 however, obliged to confess ourselves as in opposition to the great master who has estal)lished 

 rules to follow in the classification of organs, in consequence of liis having limited his com- 

 parisons to the two classps 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 wonkl have discovered it, as we have done, in the region of the shoulder, and not in that of 

 the sternum. 



