224 Zoological Society. 



The pectoralis medius seu secundus 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 arises above and between the ori- 

 gins of the pectoralis secundus and the anterior strip of the pectoralis 

 major, also partly from coracoid process ; its fibres converge to be in- 

 serted into the proximal end of the humerus, above and behind the 

 pectoralis major. 



Coraco-brachialis. — This is represented by two small strips of mus- 

 cular fibres which rise from the posterior part of the coracoideum, 

 and are inserted, one directly 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 very remarkable, 

 especially as regards the position and course of the pectoralis medius, 

 since the physiological conditions of the circumstances attending 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, I think, from this adherence 

 to a typical organization, in a very rare exception, that the teleolo- 

 gical conclusions respecting that typical construction, as it is mani- 

 fested in the general rule, are in no ways affected by such an excep- 

 tion ; because the modification of one part necessarily affects that of 

 many others, perhaps of the whole body. If, for example, the fixa- 

 tion and structure of the lungs require a broad sternum and con- 

 comitant modifications of the coracoid and scapula for the mecha- 

 nical 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 muscle 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. 



The motions of the rudimental wing and its terminal hook would 

 seem to be produced as much by the cutaneous muscles which con- 

 verge to be inserted into the integument connected with it, as by 

 the feeble representatives of the true wing- muscles above described. 



Muscles of the Posterior Extremity. 



The most superficial of the muscles on the outer side of the leg is 

 that broad thin expanded one which combines the functions of the 

 tensor vagina and rectus femoris, and also, according to some anato- 

 mists, as Cuvier and Meckel, those of the gluteus maximus ; since 

 however it is exclusively inserted into the leg, I shall describe it with 

 the other muscles moving that segment of the posterior extremity. 

 The removal of this muscle, of the sartorius, and the biceps cruris, 

 is requisite to bring into view the glutcei. 



