B I R 



(Jeferentia terminate, were introduced into the orifice of the 

 ovidiiA within the cloaca ; and it has been obferved, that 

 the hen, before coition, everts the intcftinc fo much, tliat 

 the orifice of the vagina is vilible on the ontlideof thebody, 

 which would render the infcrtion of the male organ very 

 prafticable, cfpecially in tlicife birds which are provided 

 with a penis. Ttie impregnating liquor mull be tranf- 

 niitted as far at leall as the part in which the egg is 

 clothed with the (liell ; for afterwards it would be incapable 

 of exerting any infl-.ience upon it ; and it is probable that it 

 reaches the ovum even before it acquires the whites, other- 

 wife the ftimuhis could not be in-, mediately communicated to 

 the cicatrkula. Many have fuppofcd, that the ftincn pro- 

 duced a vapour which was propagated to the ovary ilfelt ; 

 but the exiftence and operation of the aura fiminalis are now 

 generally difbelitved. 



Upon the margin of the anus of birds there is ufually ob- 

 ferved a projection which has been conlidered analogous to 

 the i/itoris. Trie academicians obfcrved, that it poflefFed ni 

 the femnle ojlr'uh the fame mufclcs wliich bi-longcd to the 

 penis. This part, from its fituation, is little expoied to agi- 

 tation or friction in venereal congrcfs, and from its covering, 

 which is the common integument of the anus, cannot be en- 

 dowed with peculiar or delicate fenfation. It may therefore 

 be looked upon as one of the examples of uniformity of plan 

 which are fj often difplayed in the works of nature, without 

 the accomphlhment of ai.y immediate or obvious effect. 



The female organs of generation of bird# fuffcr even a 

 greater alteration than the male parts, in confequence of the 

 ceflation of their fur.ftions. Before and after the period of 

 laying, has commenced, the ovary and oviduft, which in 

 their developed condition are the largell of the vifcera, are 

 fo diminutive, that they are hardly to be feen ; the ovary 

 is a very fmall mafs, which appears to be compofed of an 

 aggregation of minute pale yellow grains; the oviduft is a 

 mere membranous fubftance, with fcarcely any cavity, like 

 a degenerated blood-veflcl ; and the aperture, which at one 

 period permits the egg to pafs through it, is fo nearly- obli- 

 terated, that it is perceived with difficulty, and is fo clofe 

 that it does not fuffer the fmallell inftrument, or even air, 

 to efcape from it into the inteilinc. 



Mr. Hunter, and others, have obferved, that even the 

 fexual charaiters of fome feinale birds have entirely changed, 

 after the time they ceafed to lay. This phenomenon has 

 been remarked moil frequently ill xXxcpeafoivl. Several hens 

 of this genus have alFumed the manners and plumage of the 

 cock fo nearly, that their real fex could only be decided by 

 anatomical inipec\ion. 



Organs subservient to the Performance of the 

 Animal Functions. 



Bonci. 



The oiTeous fabric of the bodies of birds conftitutes one of 

 the mod curious and charafteriftic parts in the anatomy 

 of this clafs of animals ; being in many refpeCts fo curioufly 

 formed, that the analogy between them and the fame organs 

 of other animals can fcarcely be traced. 



The bones of birds have been obferved to vary in their 

 colour. The water birds have them of a duller white than 

 the other fpecies, in confequence of their abounding with 

 marrow. The bones which contain air, are always of the 

 fined colour, much exceeding in whitentfs the bones of 

 any quadruped : they are alfoof a harder and clofer texture. 

 Bccmann, in the voyage of Dampier, has obferved that the 

 black fowl of the ides of Capc-Vcrd, and other birds of thefe 

 illands, had black bones, and Daubenton reared fome hens 

 of this kind. The fame peculiarity has been noticed in the 



1 



B I R 



plntaih ; but fome preparations which were preferved by- 

 Mr. Hunter to illuftrate this fubjea, fliew that it is the 

 periolleum in which the blacknefs relides. 



The chemical principles of the bones of birdf, do not 

 differ from thofe of mammalia, except in there being a 

 greater proportion of the calcareous phofphat in .the long 

 bones, filled with air. The arrangement of the offcous 

 particles appears to be in layers, rather than fibres, fuccef- 

 fively formed, and clofcly applied to each other. 



The hones of ths haul, as in the other animals with ver- 

 tcbrx, confill of thofe of the cranium, or brain-cafe ; and 

 thofe which contain the organs of fenfe, or, as they are 

 commonly termed, bones of the/acf. 



The external form o/" //'<• <:rafl;«/« differs according to the 

 fpecies : a longitudinal and vertical feftion of it ufually ex- 

 hibits the cavity to be fomewhat of an ovular (liape, of 

 which tiie end next the face is rather pointed. In the owl, 

 the cavity of the cranium is an oval, with the axis nearly 

 vertical. The fame bones enter into the compofition of 

 the cranium in birds, as in mammalia ; but the futures 

 are obliterated at fo early an age in the former, that their 

 cranium commonly appear? as a fingle bore, and therefore, 

 in order to examine the bones of the head feparately, a very 

 young fubjeft mull be chofen. 



The OS frontis is originally made of two portions : they 

 form the principal parts of the roof of the orbits, and a 

 portion of the feptum which divides one orbit from 

 the other. They fend down, on each fide, a pointed pro- 

 cefs, alinofl to the bafe of the bill. The prominences 

 which are feen upon the heads of the ciijjoivary, hornhill, 

 pintaelo, and the curajfoiu, IsSc. are attached to the os frontis, 

 but were originally formed by diftinft offifications, in the 

 fame manner as the bones on the tarfns, which ferve as the 

 mould for \!ai.j'purs. The cafque of the cajfjzfary's head 

 is filled with numerous cells : in the pintado, the texture is 

 more Uke that of the other bones. 



The parietal bones are alfo in two pieces at one petiod, 

 although the diftiniflion is but rarely feen. Tiiey refem- 

 ble two femi-fpheres, hollowed out on the infide, to re- 

 ceive the brain. 



The temporal bones compofe the pofterior parts of the 

 orbits, and exhibit a remarkable depreffion between two 

 projedling proceffes, for lodging the mufcles employed in the 

 motions of the lower jaw. The zygoina is not joined to 

 the temporal bone. 



The occipital bone originally confifts of four portions ; 

 one placed fuperiorly, another below, and two laterally. 

 Vv^hen thefe are united, the bone has an annular figure, in- 

 circling the foramen magnum. The furface by which it 

 articulates with the firll cervical vertebrss, is a fingle fphe- 

 rical protuberance, which is placed upon the anterior edge 

 of the great foramen, and is received into a correfponding 

 depreffion of the atlas. The mobility of the head is much 

 encreafed by this m.ode of articulation. 



The fphenoidal bone forms the greater part of the bafe of 

 the cranium, its proceffes are lefs evident in general, than in 

 rr.ammalia, although it furniflies a remarkable one which 

 proceeds anteriorly like a llilet, and receives upon its edge 

 the ends of the inter-articular bones, and the palatine bones 

 and vomer, which are each adapted to fit this procefs, and to 

 flip along it, as the upper jaw is moved. The fphenoid 

 bone wants the pteiTgoid proceiTes, thefe belonging to the 

 palatine bones in birds. 



The internal furface of the cranium exhibits a (harp ridge, 

 which divides the cavity into two principal foffbe. The one 

 contains the hemifpheres of the cerebrum, the other, which 

 is fituated in the poltenor arnd inferior part of the cranium, 



accom- 



