THE MUSCLES. 33 



have the phalangeal joints greatly lengthened, while they are very short in the 

 Swifts, but normal in number, and proportionately of immense size in the 

 Humming-birds (7>m'/i//w.s', t'iJc.) Lack of space forl)ids the description here 

 of many interesting skeletal variations in the pelvic limbs of birds, but we must 

 not omit to notice the calcaneal and other sesamoids which may be found, 

 the first at the back of the hypotarsus, of the tarsometatarsus, and others in the 

 plantar region of the foot. In Owls and Ospreys there is a bony tendinal 

 bridge seen on the supero-anterior aspect of the tarsometatarsus, that is a rare 

 character in birds. 



Ossification is also extended normally to some other structures, as 

 the tendons of certain muscles; the rings and other parts of the windpipe 

 (trachea); a platelet surrounding the optic nerve at the back of the eye (Raven), 

 in which bird also a separate, small, siphon-shaped bone occurs in the region 

 of the outer ear, that is functionally pneumatic and leads to the mandible. 

 Osseous spurs occur also on the wings of certain birds, and the bony elements 

 of the hyoid vary greatly, but, for the reason already given, they cannot re- 

 ceive the attention here that they deserve. 



THE MUSCLE.S. 



The science of the muscles of birds is known as avian myology, and it is 

 only in a comparatively few cases or species that the entire system of muscles 

 of any bird has been written out, described, illustrated, and published. Still 

 we have considerable knowledge on the subject owing to the special researches 

 of numerous writers, past and present, into particular myological regions, as 

 the muscles of the wings; of the syrinx; the femoral region; and others. The 

 embryology, histology and physiology of the muscles of birds are all very ex- 

 tensive fields for research, and offer fully as much to be studied as these 

 sciences respectively do in man and other animals. 



Counting both single (azygos) and paired muscles, such a species as the 

 Raven presents us with no fewer than one hundred and fifty-six muscles, and 

 doubtless this number is practically the same in all typical passerine birds. 

 To pretend even to name them here would alone take several pages, and their 

 full description fill several volumes. 



The dermal systeiv of muscles is remarkably developed in all ordinary birds, 

 and there may be as many as thirteen pairs of them. They perform various func- 

 tions associated with the movement of the int«guments; the agitation of the 

 feathers; erection of crests and feathery ornaments; and, either directly or in- 

 directly, perform other offices. As a whole, they have been erroneously con- 

 sidered by some writers as simply segregations of the platysma ?n t/o ides &nd the 



