STRUCTURE OF THE HUMAN BODY 



35 



end of a narrow muscular tube, the gullet, which succeeds it, 

 and, running along the neck and through the thorax, pierces the 

 midriff, to become continuous with the large transversely-placed 

 stomach, which has thick muscular walls. This in its turn is 

 succeeded by a very long thin-walled tube, the small intestine, 

 followed by a shorter but broader large intestine, which ultimately 

 opens to the exterior. 



The whole of the gut is lined by the mucous membrane, a 

 soft reddish skin richly provided with blood-vessels. 



2. The Teeth (figs. lo and ii). — These deserve further men- 

 tion, as they present interesting adaptations to the food and 



mode of feeding, while their number and 

 form furnish important characters for pur- 

 poses of classification. 



All the teeth are imbedded in sockets, 

 the imbedded part being the fang, while 

 the projecting portion constitutes the 



Fig. lo. — Section of a Tooth 

 Cr., Crown; N, neck; FF, 

 fangs ; P, pulp cavity ; E, 

 enamel ; D, dentine ; Cm. , 

 cement. 



Fig. II.— Kinds of Teeth 

 This figure shows the eight teeth in one half of a jaw. 



crown. The greater part of a human tooth is composed of a 

 very hard substance, dentine, within which is hollowed out a 

 cavity for the sensitive pulp, richly provided with blood-vessels and 

 nerves. The fang is covered by a layer of bony material, cement, 

 while the crown is invested by an intensely hard substance, the 

 enamel. It is a matter of common knowledge that there are 

 two sets of teeth, the first or milk set consisting of twenty 

 teeth, which are replaced by the thirty-two teeth making up 

 the permanent set. Beginning with the latter, we find in the 

 front of the jaws eight chisel-edged incisors adapted for divid- 

 ing food. Outside these are the four pointed eye-teeth or 

 canines, which in such creatures as cats and dogs play an 

 important part as weapons and holdfasts. Lastly come the 



