AND OF THE PHYSICAL SCIENCES. 



14; 



DIGESTIVE ORGANS OF BIRDS. NO. II. 



Is the Number for May 1837, p. 94. was presented an outline of the digestive or- 

 gans of the Red Grouse, Tetruo Scotictis, accompanied witli a short description. The 

 subject being of tfreat importance, both in an anatomical point of view, and in refer- 

 ence to the classification of birds, the intestinal canal of a hiid of another family is 

 here fio-ured and described. It has been seen that the Grouse, and Gallinaceous birds 

 in "eneral, have an extra-thoracic dilatation of the oesophagus, or in other words 

 a crop; a powerful muscular gizzard, lined with a dense and tough epidermis ; intes- 

 tines of <'reat length ; and coecal appendages usually of a capacity equal to that of the 

 intestine. In the birds of prey there is a different arrangement, which will be shown 

 by the digestive organs of the Golden Eagle, Aqiiila Chrysaetus, here represented in 

 outline. 



In this bird, which is carnivorous, the tongue, a, is short, emarginite, fleshy 

 above, horny beneath towards the end, and papillate behind. There are numerous 

 crypts along the sides of the tongue, beneath it and anteriorly to the glottis or aperture 

 'if the windpipe, which pour forth a viscid fluid, analogous to saUva. The hyoid 

 bones, b, b, are seen in their natural situation. The oesophagus, c, d, is of great width, 

 and on the fore-part of the neck, previously to its entering the thorax, is dilated into 

 an extremely extensile sac, or crop, which has not a narrow aperture Uke the crop of 

 the Gallinaceous birds, but is simply a dilatation of the oesophagus, having the same 

 structure as it. Behind the crop, where it enters between the coracoid bones, the 

 tesophagus is a little contracted ; and at its lower part enlarges to form the proventri- 

 culus, g, g. At its upper part, the oesophagus has a thin layer of longitudinal muscu- 

 lar fibres, some of which extend over the crop. In its whole length, it is encircled 

 by transverse fibres, forming a distinct muscular coal. Its inner or mucous coat is 

 soft, smooth, and perforated by the apertures of numerous mucous crypts, the secre- 

 tion from which is copiously spread over it. This inner or mucous coat is less elastic 

 than the muscular, and when the ojsophagus is empty, is thrown into longitudinal folds. 



In the proventriculus, g, g, is a broad belt of cylindrical glandules, having a central 

 cavity, with thick walls, and a spongy or villous inner surface. Their inner eitremity 

 is narrowed, and they open on the mucous membrane by an inconspicuous ajierture, 

 placed in the centre of a small rounded eminence. The fluid secreted by these glan- 

 dules, and copiously poured out so as to cover the entire surface of the proventriculus, 

 as well as part of that of the stomach, is of a greyish-white colour, clammy, and when 

 cold having the consistence of slightly coagulated albumen. 



The stomach, h, which commences at the lower edge of the proventriculus, is of a 

 roundish form, a little compressed. Its outer or muscular coat is thin compared with 

 that of birds of other families, but yet of considerable thickness, and is composed of 

 fibres arranged in fasciculi, which are broader in their middle, or along the edges of 

 the organ, and are inseited into two thin tendinous spaces, i, one on each side. At 

 its upper part, the fibres diverge. Within the muscular coat is a thin layer compos- 

 ed of whitish interlaced fibrous tissue. The inner coat is of a softish homogeneous 

 texture, elevated into strong rugae running in various directions. It is considered as 

 analogous to the cuticle, and somewhat resembles that on the heel in man ; for which 

 reason it is named the cuticular lining, or epithelium. 



At its commencement, the oesophagus is placed directly in front when not distended, 

 but when filled inclines immediately to the light side, on which the crop hes. At 

 the lower part of the neck it inclines to the left side, passes into the thorax in the 

 centre, when the trachea, which had run along the left side, comes in front, and 

 bifurcates over it. The stomach occupies the middle and left side of the abdomen, 

 and when distended fills a very large portion of its cavity. 



The intestine is short, and of very small diameter, in proportion to that of the (esopha- 

 gus. The pyloric orifice of the stomach has a kind of knobbed valve. The duode- 

 num, or first curve of the intestine, j, k,l,\s of much greater capacity than the succeed- 

 ing portion. It is accompanied by the pancreas, which lies in its curvature, and after 

 receiving its ducts, terminates at /, immediately under the right lobe of the liver, where 

 it receives the biliary ducts. The intestine then diminishes in capacity, m, n, and is 

 convoluted, lying chiefly on the right side. Over the stomach this contracted portion 

 terminates, and the rectum commences, which is much dilated, runs along the sacrum, 

 enlarges at the end, to form the cloaca, o, which receives the urine by the two un-tcrs, 

 <;, r, and ends at the anus, p. Besides the peritoneal covering, the intestine has a mus- 

 cular, and an inner or mucous coat. The former is thickest in the duodenal portion, 

 the inner surface of which is delicately villous. On the rest of the small inte.tine 

 tre long slender villi, which, towards its lower part, become more sparse. The inner 

 surface of the rectum is furnished with numerous mucous crypts. 



The caca, in the Golden Eagle, t, t, are very diS'erent in capacity from those of 

 a Gallinaceous bird, being mere mucous sacs, scarcely more than a quarter of an inch 

 in length. They are seen to occupy the same place, namely, the commencement of 

 the rectum, t, v. The smaller figure shows the termination of the small intestine, 

 J ; the coeca, t, t ; the rectum, t, v ; the cloaca, u ; the anus, v ; and the ureters, to, w. 

 'The Golden Eagle is a bird organized for rapine; its frame is firm and compact; 

 its long and broad wings enable it to fly with great speed ; its legs are furnished with 

 strong muscles, and its claws are curved, tapering, and capable of being thrust into 

 the vitals of its victims, which it can also carry off in its talons when of moderate 

 size. But it does not feed exclusively on animals which it has itself captured, for it 

 olte'n devours carrion of all kinds. Keeping its prey down with its feet, it deprives 

 it in a rude manner of part of its hair or feathers, and then tears up and swallows frag- 

 ments of the flesh. Its bill, being hooked at the point, and sharp-edged, is obviously 

 well adapted for this use. If the subject be large it fills the stomach, and then the 

 crop and esophagus, these parts being capable of holding more than two pounds of 

 flesh. The crop is merely a recipient for the food, which is found in it quite unal- 

 tered. When the crop, stomach, and intermediate part are found filled, the solvent 

 action is first perceived in the proventricular space ; and it is probable that the secre- 

 tion from its glandules effects the solution of the food in all species, for in those of 

 which the inn^er coat of the stomach is thick and horny, there can be no effusion from 

 it. The mass of flesh, mixed with feathers, hair, and bones, being in the stomach re- 

 duced to a soft pulp, the nutritious parts pass into the intestine by the pylorus, which 

 rejects the indigestible substances. The hair and feathers are, by the contraction of 

 the muscular fibres, thrust into the (esophagus, the muscular fibres, of which contract 

 in succession, so that the pellet is ejected. In the duodenum the pulpy mass of the 

 food is further diluted by the pancreatic fluid, assumes a homogeneous appearance, 

 and is of a h-'ht red colour. On being mixed with the bile, it assumes a yellowish or 

 greenish tinti and deposits the chyle on the surface of the intestine, whence it is ab- 

 sorbed. The refuse enters the rectum, where it is diluted by the urine, and is finally 

 ejected in a semi-fluid state, of a dull green colour, mixed with flakes of white, 

 bein- projected to a considerable distance, so that the feathers be not soiled. 



The digestive organs of Vultures are similar to those of Eagles and Hawks ; but 

 various modifications are observed in those of the different species. In the Falconine 

 species generally, the intestinal canal is about three times the whole length of the 

 bird. Owls differ from Hawks in having no crop; but their cffica are much -larger, 

 and even approach in size to those of some of the Gallinaceous Birds. 



On comparing the figure and description here presented with those of the Red Grouse 

 formerly offered, it will be seen that the digestive organs of the Rasores and Rap- 

 tores differ in several essential respects. Similar differences occur in all the really 

 natural croups of birds, such as the Gemitores or Pigeons, the Deglubitores or Com. 

 rostral tribe, the Cantatores or Songsters, the Parrots, Snipes, Divers, and Ducks. 

 Prolificacy of the Blackbird — A pair of these birds built four successive nesls 

 last season upon the island in St James's Park, and succeeded in rearing seventeen 

 young ones ; the three first broods consisting of five each, and the last of two only. 

 There .annot be the least doubt as to the identity of the female, as she is well k.iowi. 

 to the person who attends them, and so tame as to take food from his hand while sit. 

 tinff on the e»gs. There were, moreover, no other individuals of the same sprcies near 

 the'place. Another isolated pair which 1 knew of raised, unmolested, tlir^-e brood. 



in a garden near my resi 

 younj 



idence, so that the Blackbird would appear to raise as many 



the Partridge, which produces only one brood in a season — Edward Bli/tit, 

 The Saturaliist." 



