53 
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 (Pl. X. XT, XII. XIV. p) is represented by two very thin trian- 
gular 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 prece- 
ding, from the osseous bridge separating the perforation from the notch ; the two -por- 
tions 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. XI. XIV. q) 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 (Pl. XI. XIV. r) arises above and between the origins 
of the pectoralis secundus and the anterior strip of the pectoralis major, also partly 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 (Pl. XIV. s).—This is represented by two small strips of museular 
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 phvsiological conditions of the circumstances attend- 
ing that muscle are wanting in the Apteryz. 
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, the 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 he 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. XIII. fig. 2. ¢), 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. 
