15 



The dissection of the extremities, both anterior and posterior, pre- 

 sents very many points of importance. Of late years, from the many 

 interesting questions arising ont of the subject of the origin of species, 

 it has become a point of extreme importance that comparisons should be 

 instituted between the development of similar structures in different 

 animals, or diverse parts of the same animal, in. order that we may 

 arrive at correct ideas of homology. Now, in the ostrich we have a bird 

 with terrestrial habits, and bearing a resemblance in the arrangements 

 of its muscles to the mammalian class of animals ; consequently it is of 

 immense importance to have a correct idea of the position and nature of 

 the muscles in his limbs. The branch of comparative anatomy which 

 treats of muscles has been very much neglected of late, although there 

 are as interesting considerations and as difficult problems involved in 

 myology as in neurology or osteology. 



The upper extremity, or wing, in the ostrich is very small, and per- 

 fectly incapable of flight ; the prolonged humerus forms a very large 

 portion of it. We find in this limb, however, the homologues of most 

 of those muscles which are of use in those birds which are fitted for 

 aerial locomotion. Coraco-brachialis forms an elongated fleshy muscle, 

 arising from the outer third of the inferior edge of the coracoid bone, 

 about two inches from its sternal articulation, it passes downwards and 

 backwards, to be inserted into an oblique line on the inner side of the 

 humerus, running downwards as far as about four inches below the 

 head. 



Biceps — a long, thin band — arises, by a distinct round tendon, from 

 the coracoid bone, above the coraco-brachialis, and also by a distinct slip 

 from that muscle. The fibres pass down straight, and are inserted by 

 a tendon, which runs on the surface of the muscle for a short distance, 

 into the tubercle on the inner side of the radius. This muscle is covered 

 by a large cephalic vein, which runs from the outer side of the fore- arm 

 to the inner side of the axilla, and terminates in the axillary vein. 



Covering the outer surface of the foramen which exists between the 

 coracoid and clavicular apophyses, is a triangular fleshy mass, with its 

 base inwards. This muscle Professor Haughton has suggested, and 

 apparently with good reason, to be the second pectoral of birds. Its 

 fibres arise from the borders of this aperture, which it blocks up, and 

 run outwards, becoming tendinous. The tendon passes in a groove over 

 the head of the humerus, winding round a trochlear surface, to be in- 

 serted into the outer part of the great tuberosity. The function per- 

 formed by this muscle evidently seems to be the elevation of the wing. 



A hurried glance at the combined coracoid bone and clavicle cannot 

 fail to suggest to the mind the appearance of the anterior part of an os 

 innominatum, of which the former represents the ischiatic segment, and 

 the latter, the pubis. The resemblance is extremely striking between 

 the obturator foramen and this aperture in the bones of the scapular 

 arch. May we not, then, consider the muscle closing this as the ho- 

 motype of the obturator, in the anterior extremity, and thus conclude 

 that the second pectoral in the fore is homotypical with the obturator 

 externus in the hinder limb ? 



