INTRODUCTION. 



The class of Birds (Airs), as represented in the present a^^e of tlie world, 

 is composed of very many species, closely related anions tliem:^elvcs and 

 distin'nii^hed bv numerous characters common to all. F<jr the puri)oses nf 

 the present work it is hardly necessary to attempt the definition of wliat 

 constitutes a hird, the veriest t\ <• heing- able to decide as to tlie fact in 

 re«'ard to anv Xorth American animal. Nevertheless, for the sake of «,n-eater 

 completeness, we may say that, compared with other chisses,^ liirds are 

 abranchiate vertebrates, with a brain filliuLj: the cranial cavity, the cerebral 

 portion of which is moderately well develoj)ed, the corpora striata connected 

 bv a small anterior commissure (no corpus caUosum developed), prosen- 

 cephalic hemispheres lari;e, the optic L)bes lateral, the cerebellum trans- 

 verselv nndtitissured ; tlie lunus and heart not separated Ity a diapliraum 

 from the abdominal viseera ; aortic arch sin^^le (the ri^lit only beim;' (h'vel- 

 oped) ; blooil, with nucleated red corpuscles, undergoing a comjtlete circula- 

 tion, beinii: received and transmitted by tlie right half of the (juadriloeuhir 

 heart to the lungs for aeration (and thus warmed), and afterwards returned 

 by the other half through the system (there being no communication be- 

 tween the arterial and venous ])ortions) ; skull with a single median convex 

 condvle, chietly on the basi-occipital (with the sutures for the most i)art early 

 obliterated) ; the lower jaw with its rami ossifying from several i)oints, con- 

 nected with the skull by the interventiim of a (piadrate bone (homologous 

 with the malleus) ; pelvis with ilia prolonged in front of the acetabulum, isehia 

 and pubes nearly parallel with each other, and the isehia usually separated: 

 anterior and posterior mendiers much ditferentiated ; the former modified for 

 flii»ht, with the humerus nearlv i)arallel with the axis of the bodv and con- 

 cealed in the muscles, the radius and ulna distinct, with two ]iersistent carjtal 

 bones, and two to four digits; the legs with the V>ones peculiarly cond)ined, 

 (1) the proximal tarsal bones coalescing with the adjoining tibia, and (2) 

 the distal tarsal coalescing with three (second, third, and fourth) meta- 

 tarsals (the first metatarsal being free), and forming the so-ealled tarso- 

 metatarsus ; dermal appendages developed as feathers : oviparous, tlie eggs 

 being fertilized within the body, excluded with an oval, calcareous shell, and 



^ W«' art' iii(lrl»t('(l to Pn)ft*ssor Tlu'odon' X. (lill for tlir pn'sciit arcount of thi" charactfiisties 

 of the class of liinls as «listinrrui.slit'«l from otli«'r vcrtt'liratt's, juij^'cs xi -xv. 



