586 SPECIAL PHYSIOLOGY. 



exists, being sometimes very large, but sometimes short and bifid. The car- 

 nivorous Marsupials have no caecum, and the insectivorous species a small 

 one ; in the frugivorous species it is wide, and twice as long as the body, and 

 in the herbivorous species three times as long. 



The narrow part of the caecum, the vermiform appendix, present in Man, 

 exists in the apes and gibbons, and in the marsupial wombat, but in no other 

 mammalian animal. 



In the Monotremata, a small caecum alone indicates the place of junction 

 of the small and large intestine ; the intestinal canal is narrow, but widens 

 below, and ends in a cloaca, as in birds. 



Birds. The digestive canal in Birds is usually complex, the oesophagus 

 being more or less dilated near its lower end, to form the crop, or ingluvies, to 

 which succeeds the proventriculus, or proper secreting stomach ; and beyond 

 this is a third cavity, forming the gizzard. In the pelican, the floor of the 

 mouth, and in some other birds, the sides of the fauces, are dilated into recep- 

 tacles for food. 



The (Esophagus varies in length according to that of the neck. In the 

 storks, herons, and pelicans, which swallow their prey whole, it is very wide ; 

 and in the cormorant, it forms a large pouch. It communicates freely with 

 the proventriculus, and its longitudinally plicated mucous membrane has 

 numerous follicles, which secrete a mucus to moisten the food, and aid in 

 deglutition. The crop, or dilated portion of the oesophagus, is not distinct in 

 the toucans and hornbills, or in frugivorous and insectivorous birds, or in 

 most of the waders. It is even wanting amongst the swimming birds, in the 

 swans and geese, but is small in the ducks. The large birds of prey have a 

 small crop, lodged in front of the furcular bone or merrythought, at the root 

 of the neck. The crop is most developed in the grain-eating gallinacea, form- 

 ing a dependent bag connected with one side of the oesophagus, as in the fowl, 

 or, as in the pigeons, consisting even of two lateral oval sacs. Where a crop 

 exists, the short portion of the oesophagus below it is named the second or 

 lower oesophagus ; it gradually dilates into the proventriculus, which has no 

 constricted cardiac orifice. 



The proventriculus^ also called the ventriculus succenturiatus, the true glandu- 

 lar stomach, varies in form and size in different birds, being sometimes wide 

 and straight, and sometimes round. In the rasorial birds, it is wider than the 

 oesophagus, but smaller than the gizzard ; in the birds of prey, it is about the 

 same size as the gizzard ; in the parrots and storks, it is larger than the giz- 

 zard, and in the ostrich, four or five times as large. Its mucous membrane 

 is thicker and more vascular than that of the oesophagus or even of the crop, 

 and, as in the mammalian stomach, is provided with numerous gastric glands 

 arranged perpendicularly to the surface, sometimes simply tubular, as in the 

 carnivorous eagle and sea-gull, the insectivorous swallow, and the granivorous 

 pigeon, and often sacculated, or even expanded into compound follicles, as in 

 other grain-eaters, viz., the fowl, turkey, rhea, and ostrich. The disposition 

 of these glands on the interior of the proventriculus, differs in different Orders, 

 and even in different genera of the same Order. Thus, they may be diffused 

 over the whole surface, or may form a single oval, elongated, or triangular 

 cluster, two oval lateral clusters, or four arranged in a circular manner, or 

 they may form a zone or belt. 



The gizzard, gigerium or ventriculus bulbosus, the third, last, or muscular stom- 

 ach of birds, is a more or less flattened, ovoid receptacle, having two neighbor- 

 ing apertures at its upper part ; one, into which the proventriculus opens, and 

 the other leading into the intestine. Between and below, as it were, these 

 apertures, the gizzard forms a cul-de-sac, varying in size, and having walls of 

 variable thickness in different species. In the birds of prey, the muscular coat 

 is thin, and its fibres radiate from two lateral tendinous centres. It is in the 

 rasorial and flat-billed swimming birds, as exemplified in the fowl and swan, 

 that the gizzard is most developed ; the deep red muscular fibres here form 

 four very thick masses, two of which, named the musculi laterales, constitute 

 the sides of the gizzard, whilst two smaller ones, the musculi intermedii, are 

 placed at one end ; they all radiate from, and towards, two very strong anterior 

 and posterior tendons. The cavity of the gizzard is comparatively small, and 



