446 TEE DIGESTIVE APPARATUS IN MAMMALIA. 



(Gray concisely remarks : "When deii-lutition is about to be performed, the 

 pharynx is drawn upwards and dilated in different directions, to receive the 

 morsel propelled into it from the mouth. The stylo-pharyngei, which are much 

 further removed from one another at their origin than at their insertion, draw 

 upwards and outwards the sides of this cavity — the breadth of the pharynx, in 

 the autero-posterior direction, being increased by the larynx and tono'ue being 

 carried forwards in their ascent. As soon as the morsel is received in the 

 pharynx, the elevator muscles relax, the bag descends, and the constrictors con- 

 tract upon the morsel and convey it gradually downwards into the a-sophagus.) 



The deglutition of liquids is carried on in a similar manner. 



It is curious to remark that, in Solipeds, the food does not come into direct 

 contact with the greater portion of the superior wall of the pharynx during its 

 passage through that cavity. When the alimentary mass is carried back by the 

 tongue, it raises the soft palate and bears the posterior border of this backwards 

 to the entrance of the oesophagus. The extreme development of this palatine 

 curtain, therefore, quite prevents this surface of the pharynx from being directly 

 applied to the food, and it is through the medium of this partition that the 

 constrictors exercise their peristaltic action on the morsel of aliment, until it 

 reaches the oesophageal orifice. 



Differential Characters op the Pharynx in the other Animals. 



The iiharynx nf Ruminants is elongated and very spacious. The hj-o-, thyro-, and crico- 

 pharyngeal muscles— the middle constrictor aud inferior constrictors— are less distinct from 

 each otiier tlian in the Horse: the inferior constrictor is very small, and the fibrous raphe on 

 which the constrictors unite is little developed. In the pharynx of the Ox and Sheep is 

 noticed a mucous fold that descends to the middle of the posterior wall, and appears to be a 

 continuation, posteriorly and inferiorly, of the nasal septum; whence results the formation of 

 two glanduhir pharyngeal caeca at their bottom. 



In t ie Camel, this organ is remarkable for the large dimensions of its longitudinal direc- 

 tion and its relative narrowness. The posterior pillars of the soft i)aLite unite at a great 

 distance above the entrance to the cesophafrus, and the pharynx appears to be divided into two 

 compartments by a transverse mucous fold, which is detached from the posterior wall. The 

 superior compartment thus formed, shows, above, the guttural openings of the nasal cavities — 

 openings which are narrow and vertically elongated — and the orifices of the Eustachian tubes ; 

 while iit the bottom of the inferior compartment is the oesophageal infnndibulum and the 

 entrance to the larynx. The pharyngeal mucous membrane in this animal is black in colour. 



In the Pig, the f)haryngeal caecum is sacculated, and its mucous membrane is very vascular, 

 and rich in closed follicles. 



In the Dog, the infundibulum is very spacious. The posterior pillars of the soft palate 

 subside on the walls of the pharynx befce reaching the entrance to the oesophagus. The 

 pharyngeal mucous membrane, much finer than that of the oesophagus, is distinguished from 

 it by a sharp line of de:tnircation, and here it is very rich in glands. The crico-ph.tryngeal is 

 not very distinct from the tljyro-pharyngeal muscle; so that, in reality, only three constrictors 

 can be distinguished. 



Comparison of the Pharynx of Man with that of Animals (Fig. 253). 



In consequence of tlie smallness of the soft palate, the pharynx of Man is only a kind of 

 channel between the mouth and the larynx and oesophagus. It is usually divided into three 

 portions : a superior, the posterior nares, covered by ciliated epithelium ; a middle, or guttural, 

 and an inferior, or oesophageal. The two latter are covered with tesselated epithelium. 



The muscles are almost the same as in the Dog, being a portion of the jialato-pharyngeus, 

 the superior, middle, and inferior constrictors, and a stylo-pharyngeal muscle. 



Below the sides of the pharynx, and between the pillars of the soft palate, are the 

 amygdalae — almond-shaped organs, the surface of which shows the openings of the follicles 

 that, with the vessels and a little connective tissue, compose their substance. 



