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mfccrtaining the fituation of the fpleen, it lias been uniformly 

 difcovcTffd underneath the left lobe of the liver, placed a 

 good deal backwards, and on the right fide of the zone of 

 gaftric glands. Its peritoneal connetlions to the neighbour- 

 jiig parts are loofe and permit it to be difplacej, when the 

 other vifcera are removed from their fitiiations, which cir- 

 cumdance may have occafioned fome difference in the ob- 

 fcrvations made upon the fuhjeft. The fituation we have 

 defcribcd is the moll convenient tor its being fi-.pplied with 

 bUiod, which it receives from the gadric artery, and is btfides 

 coiifillent with general analogy. 



The figure of the fpleen is mod commonly round ; it is, 

 however, in iome birds, a little different in form. The mofl 

 ufual deviation is the oval or kidney (hape, which has been oh- 

 erved in the conror/7nl,lhe eagk, the pintado, the common fonvl, 

 &c. In the cftr'u-h it is cylindrical, and in the cajfoivary it has 

 been hkened'in figure to a foal fid:. In the ^u// it is much 

 elon5Tated,and pointed at both ends, as it is fliewn in PlaUlV . 

 in the Annlomy of B':rdu and /7f . f>. 



The fpleen affumes rather an irregular form in \\\f: gcofe ; 

 it is fli"htly comprefTed and roinid oti the one fide, and flat 

 on the other. The outline prefented on either fide is tri- 

 angular, and one of the angles is prolonged as a mamillary 

 procefs, which is dillinguiihcd from the reft of the fpleen by 

 a flight cleft or fifTure. This is reprefcnted in fg. 7. of 

 Plate IV. of the Annlomy of BhJ.s ; a the body of the fpleen 

 viewed on the flat farface ; i the papilla-fliaped procefs ; f 

 the entrance of tl'.e fplenic artery, upon the edge ; (/the vein 

 penetrating the flat furfaee. 



The texture of the fpleen is fo much more clofc and firm 

 in birds than mammalia, that one might be eafily led to 

 fuppofc its ftructurc was different ; but when prepared by 

 being injeifled with coloured fubllances, and fiibmitterf to 

 examination through a lens, we havedifcovered, as in matr.- 

 malia, the fpknic artery to terminate in numerous minute 

 branches, and the veins to take their rife from cells. The 

 only difference which exifb, is with refpeft to the magnitude 

 of the cells, which are extremely minute; and thence arife 

 the peculiar compadnefs and denfity of the fpleen of 

 birds. 



The flrudlure of this organ being fo very fimilar to that 

 of the fpleen in mammalia, it is fair to conclude that their 

 funflions are a'fo analogous. The fituation of the vifcus in 

 b'rds might be confid;red, therefore, as affording an objec- 

 tion to that theory, which fuppofes this organ was defigned 

 to regulate the quantity of blood employetl by the arteries of 

 the liomach du^ mg the fecrction of the gaftric fluid ; for, in 

 birds, the fpleen receives no prefTure as occurs in mammalia 

 bv the introduction of food into the ftoniach, and confe- 

 qiiently, cainot affeft the diilribution of the blood in the 

 collateral arteries, more under the circumftance of a full 

 ftomach than an empty one. In order to put the fpleen of 

 birds in the fame conditions to which it is fubjecl in man and 

 q'ladrupeds. it flioulJ be phiced under the crop in the gra- 

 minivorous tribe, or between the ventricle and the ribs in the 

 other kinds. 



Ahhough it would be often WTong to determine the ufcs 

 of an orofan in one clafs of animals, from the circuinftanccs in 

 which it may be placed in another ; yet no theory can be 

 confidered as well founded, unkfs it be framed in the con- 

 tsmplation of all the varieties of comparative ftru<3ure. 

 yflforhents. 

 One of the mofl remarkalile and inexplicable circum- 

 flanccs in the anatomy of birds is, that the rutritious 

 fluid of the intetlines, or the chy'e, is as trai^fparent as 

 the lymph which is taken up from, the common interllices, 

 cr the furfaee of the body. The abforbents of the iutcf- 



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tines, thfreforc, do not deferve to be called laBeaJs, an ap- 

 pellation they have received iu man and quadrupeds, in con- 

 fequence of the opacity and milky appeai-auce of their cou- 

 teiif:. 



The difcover)' of the lymphatic fyflem in birds may be 

 reckoned amoiigll the modern improvements in anatomy. 

 Before Mr. Hunter, about the middle of the laft century, 

 del.jribed the abforbents of the neck, it was generally fup- 

 pofed that the office of thefe veffels was fulfilled in birds by 

 the mmute branches of veins. This opinion was rendered 

 the more probable as feveral able anatomiffs had fought in 

 vain forthofe white veffels, and their glands, which are fo eafi- 

 ly deteded in tire mefentcryof the fmalleft quadruped. It was 

 not then known, however, that the lymphatic veffels of the 

 intcflines were always pellucid in birds, and unprovided with 

 glands, and accordingly Mr. Hunter's difcovery was not ge- 

 nerally admitted as decifive or. the queftion, until fome years 

 afterwards the whole of the lymphatic fyflem had been de- 

 fcribed by Mr. Hewfon ; he employed for this pui-pofe a 

 ynur^g and vrry lean goofe, which had been recently fed, 

 and having fecured it upon a table, he opened the abdomen 

 whilll the bird was yet alive, and paffing a ligature round 

 its mefenteric veffels, as near to the root of the mefcntery as 

 pofTible, the lymphatics of this part became apparent in a 

 few minutes. Ttie fame method alfo was purfued to cxpofe 

 the abforbents of the neck. A ligature was placed round 

 the jugular vein at the lower part of the neck ; and to be 

 moi'e certain of inclofing the lym)ihatics which are near it, a 

 fuflicient quantity of the furrounding fubllance was included 

 by the ligature. In this way he fucceded in tracing the lym- 

 phatic fyllem, in more inllances than one, after having filled 

 the veffels with quickfilver. He publifiied a defc.iption of 

 the abforbents, lUullrated by two drawings, in the Philofo- 

 p'ical Tranfaftions for the year J74S, and in his Experi- 

 mental Inquiries into the lymphatic fyftem. 



As no accounts or figures of the abforbents of birds 

 have been offered to the pubhc fince Mr. Hewfon's time, 

 we cannot do better than adopt the dcfcription, and 

 copy "le reprcfentation left to us by that inJ.cfatigable 

 anatomiil ; in doing which, we fliall tranfcribe his own 

 words. 



" This fvflem confifls in birds, as :t does in the human 

 " fubjcfl, of three parts, viz. the lafteals, the lymphatic 

 " vsfL-ls, and their common trunk, the thoracic duct. The 

 " latl^-als indeed, in their llriAeft fenfe, are in bii-ds, 

 " the lymphatics of the inteflines, and like the other Ivm- 

 " phatics, carr)' only a tranfparcnt lymph ; and inftead of 

 " one thoracic duft there are two, which go to the two 

 " jugular veins. In thefe circuinftanccs, it woul.l feem, 

 " that birds differ from the human fuhjift, fo far at leaft: 

 " as I may judge from the diiTeftion of a goofe, which was 

 " the bird I chol'e as moft proper fi)r this inquiry, and fi'om 

 " which I took the following dcfcription, after previoufly 

 " iiijefting its lymphatic fyllem with quickfilver. 



" Theladeals run from the intelliues upon the mefenteric 

 " veffels. Thofe of the duodenum pafs by the fide of the 

 " pancreas, and probably receive its lymphatics : afterwards 

 " they get upon the cahac artery. Whilll they are upon 

 " this artery they are joined by lymphatics from the hver. 

 " Here they form a plexus, w hich furrounds the coeliac 

 " arterj' : at this part they rxccive a lymphatic from the 

 " gizzard ; and a little farther, another from the lower 

 " psrt of the oefophagus (or zone of gaftric glands). Hav. 

 " ing now- got to the root of tlie coeliac artery, they are 

 " joined by the lymphatics fiom the glandular renalcs, or 

 " renal cnpfules ; and near the fame p^rt, by the ladeals 

 " from the other fmall inte.lines, which veflels accompany 



7 «' the 



