20 



THE HUMAN MECHANISM 



with the axial skeleton by muscles only. A wide range of 

 movement is thus secured at the shoulder joint. 



13. Organs of digestion. The digestive system consists es- 

 sentially of a long tube, the alimentary canal, passing through 

 the body. 1 Into this tube, at various points, ducts from a 

 number of glands pour digestive juices. The alimentary 

 canal begins with the mouth cavity 

 and its familiar organs, the teeth, the 

 tongue, etc. ; this cavity opens pos- 

 teriorly into that of the pharynx, 

 into which also opens the nasal 

 cavity, separated- from the mouth 

 only by the palate (see Fig. 14). 



On the ventral side of the pharynx, 

 just beyond the root of the tongue, is 

 the slitlike opening of the windpipe 

 (see sect. 14) ; posteriorly the pharynx 

 is continued in the long gullet, or 

 oesophagus, a tube which passes down- 

 ward through the neck and thorax 

 FIG. 14. Diagrammatic me- (within the mediastinum) to join the 



dian dorsoventral section stomach, which it enters immediately 

 of the nasal and throat ,, . , , , ,. , 



after passing through the diaphragm. 



The stomach is a large pouch with 

 contractile walls permitting adapta- 

 tion of its size to the bulk of food 

 it may contain. Its situation is shown 

 in Fig. 155, which also shows how it 

 opens on the right side of the body into the very long, 

 coiled small intestine. The coils of this part of the tube 

 may be followed for from twenty to twenty-four feet, to the 

 large intestine, into one side of which it opens. The large 

 intestine, or colon, consists of three portions: the first ascend- 

 ing on the right side to the general level of the stomach, the 

 1 See Fig. 155 for the general arrangement of the organs of digestion. 



passages 



C, nasal cavities; M, mouth 

 cavity; T, tongue; E, epi- 

 glottis; G, glottis, or opening 

 from the pharynx into the 

 trachea; U, the end of the 

 soft palate ; 0, oesophagus 



