INTRODUCTION. ix 



chains, continents, or the trackless ocoan. Though tho muscles of 

 the extremities of birds are generally short and thick, the tendons are 

 longer and slender, dense, and often ossified. The form and move- 

 ments of birds being nearly the same, there is a great uniformity in 

 the disposition of their muscles. Their arms and hands being appro- 

 priated for flight, their progressive motion through the air depends 

 chiefly on the action of ^h* pectoral is major or the humerus, a muscle 

 surpassing in magnitude all the rest in the body and covering nearly 

 the whole of the forepart of the trunk. The muscles of the arm, the 

 forearm, and the hand are inserted high up, and their fleshy portions 

 confined to near their orifice, so that only the long tendons are sent 

 down to the points which are to be moved. There is very little motion 

 in the phalanges of the fingers. 



It is not within the scope of this introduction to give an exhaus- 

 tive or detailed classification of the organs of birds. The osseous 

 system or the organs of support has been touched upon, also the 

 tegumentary organs and those of motion. To detail the organs 

 of connexion, sensibility and sensation as well as of nutrition and 

 generation would go far beyond the intended limits of this in- 

 troduction, while the proper treatment of these would need a more 

 competent writer. En passant, however, a few remarks may not be 

 out of place, especially in reference to those organs which the 

 ornithologist and the student must neeessarily examine for 

 instance, the testes. These, it is generally known, lie in front of, and 

 in close proximity to, the kidneys, and although there are certain 

 external characters which would enable the determination of the sex 

 of a bird, yet nothing would be more satisfactory than an exa- 

 mination of this organ of generation testes or ovaries decide 

 the question beyond doubt. During the breeding or pairing season 

 the testes of all male birds are much developed, while the female 

 sex exhibit in the same situation well-developed ovaries which 

 at other times though present, are small and granular. External 

 sexual differences are more marked in birds than in mammals 

 and other vertebrates; but these are not always reliable, especially 

 in the case of birds, the young and the males of which assume 

 the plumage of the female, or vice versa, at different seasons of 



