B I R 



f, b, the two crops, c the contrafted part of the cefo- 

 phagns. 



In fome fpecies, as the pouting pigeon^ the oefophagus 

 above the crops, is of fuch great dimenfions, that the latter 

 are hardly difcernible ; thele birds alfo have the power of 

 dillending their oefophagus with air, which gives them that 

 grottfque appeal ance from whence they derive their name. 

 A capacious crop is more necefTary to the pigeon than other 

 birds, both becaufe its food requires long maceration, and 

 becaufe the young, and even, on fome occafions, the female, 

 draw their fubfiftence from this repofitor)-. The extraordi- 

 nary-change which occurs in the itrnCture of the inner mem- 

 brane of the crops of the pigeon, by which a milky fluid is 

 fecreted, for the nouriihmcnt of the young birds, will be 

 defcnbed in its proper place. 



Although there is all the variety in the form of the 

 oefophagus we have defcribed, the internal ftrudure appears 

 to be the fame in all birds. Belidcs the external cellular 

 covering, by whicii it is connetled to the adjacent parts, it 

 pofTefTes a 'mufcular coat, an internal vafcular tunic, and a 

 cuticular lining. The mufcular coat coniiils of two layers 

 of fibrei ; in the external layer thtfe are tranfvcrfe, or more 

 properly circular ; the other llratum is compofed of longitu- 

 dinal tibres. The mufcular coat is moil Itrongly marked 

 at the top of the tube, where the actions of degluLition com- 

 mence, and upon the crops, where fupport and motion are 

 required. The internal coat refembles in llrufture that 

 which is ufually met with upon the inner parts of cavities, 

 with this difference that it is provided in birds with an extra- 

 ordinar)' number of follicular glands, wh ch pour out their 

 fluid through numerous foramina, r^fcmbhng pin-holes, 

 upon the internal furface. Thefe glands fecrtte a quantity 

 of mucus, which is employed in macerating the food, 

 while it is detained in the celophagus, or crop. This fecre- 

 tion is remarkably copious. Spallanzani introduced a piece 

 of fponge into the crop of a pigeon ; and after it had re- 

 mained there twelve hours, he cxpreffed from it above an 

 ounce of mucus, and the quantity obtained from a turkey, 

 amounted to feven ounces in ten hours. The follicular 

 glands are moll numerous at the commencement of the oefo- 

 phagus, and towards the termination of this tube in the llo- 

 mach, the inner fui-face of the craw is but fparingly fupplicd 

 with them. See Plate I. of the Anatomy of Birds, Jig. 2. in 

 which the oefophagus and crop are inverted, for the purpofe 

 of exhibiting the orifices of the mucous follicles, and in /%. 3. 

 they alfume a btau'iful and regular appearance below the 

 dilated parts of the oefophagus. It is very common for the 

 mucous glands to be affembled in a regular and marked man- 

 ner round the very termination of the oefophagus, as a in 

 Plate II. Jig. 2. of the Anatomy of Birds. 



The cuticle, which inveilsthe oefophagus, is generally fo 

 thin and tender, that it might efcape obfervation. It is, 

 however, fufficiently plain in many large birds, and almoft 

 always vifible, upon the iniide of the crop or the other di- 

 lated parts, which are more expofed to friftion from extra- 

 neous fubftances. The infenfible lining of the oefophagus ter- 

 minates abruptly at the zone of gailric gland;. 



It may be remarked with retpeft to the oefophagus of 

 birds,"that its chief pecuharities confiil in the great fize, oc- 

 caGonal enlargements, and number of mucous glands. Thefe 

 circumllances neceffarily depend upon the very lingular flruc- 

 ture of the ftomach, which we fhall next defcribe. 

 Stomach, 



The organ of digeRion in birds confifts of two parts ; one 

 for producing the digeftive fluid ; the other the receptacle 

 in which the cor.verfion ot the food is effefted. The ap- 

 paratus for the fecretion of the gailric juice is called, 



B I R 



TLt Bulbils glandulofus, or the Zone of Gajlric Glands. — 

 This part is fituated at the termination of the oefophagus, 

 and appears in moll inftances to be the continuation of that 

 tube. It has the fame cellular and mufcular coa:s, whicli 

 oblcure its real ftrufture, when perceived externally, efpcci- 

 ally in the graminivorous birds, which have ilrong mucles 

 upon the oefophagus. When the outer tunics are removed, 

 a number of fmall glandular bodies arc expofed, arranged 

 with the mo.l perfect regularity, and clofcly applied to each 

 other. They affume an indiitindl granular appearance in 

 Imall birds generally, and even flill more fo in thofe which 

 fubiill on animal food, as the accipitrine and pifcivorous hivds; 

 but in the gallina, and the large graminivorous -water birds, 

 as theywi^n, the goof, &c. the gailric glands, when divtfted 

 of their coaf:, are readily difcovcred, by the naked eye, to 

 be fmall cylinders, or tubes, placed hori20ntally with refpcdl 

 to the parictes of the ftomach ; the external end is clofcand 

 of a round figure ; the internal extremity of the tube is 

 fomewhat concave, and cont?.i.iS a fmall foramen, which is 

 applied to a correfponding hole in the internal membrane of 

 the bulbus glandulofus. See Puile II. m the Anatomy of 

 Birds, Jg. I. « rtprefents a number of the gaftric glands, 

 with their external extremity expofed, by a portion of the 

 mufcular coat beir.g removed ; and in_/%. 2. 6 Ihews the ori- 

 fices of thele glnds upon the internal coat of the ilomach, 

 and c the cut edge of the bulbus, with the cylii.ders as they 

 are placed between the mufcular and ir.temal coats. The 

 fubjtft of both the figures is the •wildfwan. 



The gailric glands commonly encncle the beginning of 

 the itomach as a pcrfecl and equal zone. In fome ii.ftances, 

 however, where they are not large, as in the rapacious and 

 pifcivorous birds, they are more numerous at one part of the 

 llomacii than another; ke P/ate lll.Jg.2. which exhibits 

 the ftomach of the heron, b b the gaftnc glands. 



The form of the bidbus is not quite regular in the ojlrich; 

 the ftrutture of the glands alfo is not the fame as in other 

 birds : inftead of being placed in regular and dole order, 

 t.'icy are dilpofcd in maffes of an unequal form ai.d iize, 

 feparated tor fome dillance from each other. On making a 

 feclion of the maffts, they are found divided or interrupted, 

 by proceffes of ftrong white cellular fubftance ; from which 

 it would Icem, that they are compofed of fcveral glands, 

 although there is b'.:t one foramen belonging to each inafs on 

 the internal tunic or the bulbus. The magnitude of the ori- 

 fices of the gaftric glands, even exceeds the proportion to be 

 cxpeAcd from the lize of the bird ; being capable of receiving 

 the head of a Lrge pin, they Hand at the dillance of about 

 the J of an inch alunder, and do not open with perfcft re- 

 gularity upon the i:iternal fl^face of the ftomach, being 

 mofl croivded towards the centre, where alfo their apertures 

 are largell ; the internal tunic of the oftrich, from thefe cir^ 

 cumllances, exhibits a «orm-eatei! appearance. 



The gaftric glands in all birds, like other parts, which 

 produce an .important fecretion, are endowed with aa ex- 

 treme degree of vafcularitv. 



Some authors have defcribed a cuticuLir coal, on. the in- 

 ternal furface of the bulbus glandulofus, which they have 

 compared to velvet on account of its foft and fpurgy tex- 

 ture ; it appears, however, very doubtful, whether this cover- 

 ing Ihould be conlidered a tunic or not; we have obfervcd 

 that it is readily detached, and loluble in wiiter ; it certainly 

 bears no refemblance to the cpidcnnis of the cefopliagus, and 

 ftill lefs to the fubllauce which iuvells the rcmaiuing portion • 

 of the ftomach, or gizzard. 



No very latisfaftory experiments have yet been made up- 

 on the nature ol the digellive fluid of birds. When it is ex- 

 prtffed from the gaftric glands, which is the only mode of 



obtain- 



