582 SPECIAL PHYSIOLOGY. 



bull have even been described in the Entozoa and Rotifera. No such glandu- 

 lar structures exist in the Coelenterata. or Infusorial Protozoa. 



The Pharynx and Gullet, and Deglutition in Animals, 



The parts concerned in deglutition and the act itself, are similar in all the 

 air-breathing Yertebrata, but both become gradually simplified. The uvula is 

 absent, excepting in the higher Quadrumana. The soft palate is very large in 

 the elephant and the Cetacea. Tonsils are always present. In all cases, from 

 the highest Mammalia down to the Amphibia, the pharynx communicates 

 with the cavities of the mouth, larynx, and oesophagus, and also, on each 

 side, with the tympanum. In Mammalia, the structure of its walls resembles 

 that in Man, and in the second stage of deglutition, it rapidly and safely trans- 

 mits the food and drink into the oesophagus, over the laryngeal opening, whilst 

 the third or cesophageal stage of deglutition is also, as in Man, performed more 

 slowly by waves of peristaltic contraction, even against gravity, as is seen in 

 the horse when drinking. In Birds and Reptiles, the pharynx is of simpler 

 construction and action, being in the Serpents enormously dilatable. In the 

 Amphibia, it approaches the less defined character which it presents in Fishes. 



In Fishes, which respire in the water by gills, the pharynx has no commu- 

 nication with the nasal fossae, and, moreover, the larynx and air-breathing 

 apparatus are absent, except, in some cases, the air-bladder ; hence the phar- 

 ynx forms a mere infundibular passage, leading from the mouth into the shut 

 oesophagus ; but its sides are supported by the cartilaginous or bony frame- 

 work of the branchial arches, between which are the branchial openings ; be- 

 sides this, there are special pharyngeal bones, which, as already mentioned, 

 often bear prehensile or even masticatory teeth. 



In the Molluscous, Annulose, and still lower Classes, a special pharynx is 

 seldom distinguishable ; but the buccal cavity usually passes directly into the 

 oesophagus. In the Molluscoida, however, a part called the pharynx exists 

 between the mouth and the oesophagus. 



A true pharynx is indeed characteristic of the Yertebrata, and is specially 

 developed in those which respire air, and in which the food has to be swal- 

 lowed, without entering the sensitive air-passages, and with but a momentary 

 interruption to the breath. In the cold-blooded Serpents, however, which 

 swallow animals entire, deglutition is painfully slow, and causes a certain in- 

 terference with respiration. In the young kangaroo, whilst it is still retained 

 in the marsupium or abdominal pouch, the upper part of the larynx is elong- 

 ated, and projects, as in the Cetacea, into the posterior nares, so that the milk 

 passes down on each side, without risk of entering the air-passage, and with- 

 out interference with the act of breathing. 



The Stomach and Intestines in Animals. 



Mammalia. In the Quadrumana, the stomach often resembles that of Man, 

 but it is sometimes globular or elongated, sacculated, constricted, or bent on 

 itself ; a cardiac and a pyloric portion are always recognizable. In the Car- 

 nivora, the stomach also presents the human shape, but the cardiac pouch is 

 large. In the insectivorous Cheiroptera, it is globular ; in the vampyres, it 

 is long and conical, the cardiac end being the larger ; in the frugivorous spe- 

 cies it is still longer, the cardiac pouch is constricted in its middle, and the 

 pyloric portion is bent. In the proper Insectivora, this organ is elongated. 

 In the Edentata, it is usually simple ; but in the genus Manis, the cardiac and 

 pyloric portions are marked oft' by an internal fold, and, in one species, a long 

 sac extends from the pyloric portion. In the sloths, the stomach is first di- 

 vided into a cardiac pouch and a pyloric portion ; the former has a dense epi- 

 thelium, and is again subdivided into two parts, one ending in a blind canal ; 

 the pyloric portion has thick walls, and a soft mucous membrane, and is sub- 

 divided into two parts, which might be compared with the third and fourth 

 stomachs of the Euminants. In the ant-eaters, the cardiac part of the stomach 

 constitutes a kind of crop, whilst a second chamber, having thick walls and a 

 hard gristly lining, somewhat resembles the yizzard of the bird, and, compen- 



