OF THE SOUTHERN APTERYX. 289 



lowest development in the Apteryx, are nevertheless similar in number and arrangement to 

 those which in some birds of flight are known to outweigh all the other muscles of the body. 



The pectoralis major (PI. XXXI. XXXII. XXXIV. XXXV. p) is represented by two 

 very thin triangular layers of muscular fibres, the anterior of which is three lines broad 

 at its base, and is attached to the sternum immediately exterior to the perforation of 

 that bone: the second, posterior, and somewhat narrower portion, rises immediately 

 behind the preceding, from the osseous bridge separating the perforation from the notch ; 

 the two portions converge as they extend upwards and outwards to unite and be inserted 

 into the anterior and internal surface of the proximal third of the humerus. 



The pectoralis medius seu secundus (PL XXXII. XXXV. 5) is a similar, thin, feeble, but 

 broader triangular layer of carneous fibres, which arise anterior to the preceding, just 

 below the coracoid socket of the sternum, and converge as they wind over the shoulder- 

 joint to be inserted into the upper surface of the proximal extremity of the humerus, 

 of which they thus become an elevator. 



The pectoralis minor seu tertius (PI. XXXII. XXXV. r) arises above and between the 

 origins of the pectoralis secundus and the anterior strip of the pectoralis major, also partlv 

 from the coracoid process ; its fibres converge to be inserted into the proximal end of 

 the humerus, above and behind the pectoralis major. 



Coraco-brachialis (PI. XXXV. *■). — This is represented by two small strips of muscular 

 fibres which rise from the posterior part of the coracoideum, and are inserted, one di- 

 rectly below the other, into the proximal third of the humerus. 



Obs. — The close adherence to the ornithic type of the muscular system of the anterior 

 extremity in the Apteryx is more especially remarkable as regards the position and course 

 of the pectoralis medius, since the physiological conditions of the circumstances attend- 

 ing that muscle are wanting in the Apteryx. 



Here we have a true bird, exhibiting a remarkable modification of the whole ornithic 

 structure, in reference to exclusively terrestrial life and nocturnal habits; and we 

 learn, from this adherence to a typical organization, in a very rare exception, that the 

 teleological conclusions respecting that typical construction, as it is manifested in the 

 general rule, are in no ways affected by such an exception ; because the modification of 

 one part necessarily affects that of many others, perhaps of the whole body. If, for 

 example, tJie fixation and structure of the lungs require a broad sternum and concomi- 

 tant modifications of the coracoid and scapula for the mechanical part of the respiratory 

 process, then it may be more convenient for the levator of the humerus to rise below 

 that bone from the sternum, and act in the due direction by a modification of its course ; 

 although the locomotion of the bird may in no way be facilitated by the aggregation of 

 muscular substance beneath the centre of gravity, nor the size of the levator be such as 

 to render its particular position a matter of any consequence in regard to that centre. 



A minute flexor (PI. XXXIV. fig. 2. t), wanting the attachment to the scapula which 

 exists in birds of flight, and arising solely from the humerus, glides along the front of that 

 bone, chiefly as a delicate tendon to be attached to the inner part of the head of the ulna. 



