500 MANUAL OF ZOOLOGY SECT. 



part of the oesophagus. The posterior part, or abdomen, 

 contains the stomach and intestine, the liver and pancreas, 

 the spleen, the kidneys, ureters, and urinary bladder, and 

 the organs of reproduction. 



The teeth are lodged in sockets or alveoli in the pre- 

 maxillae, the maxillae, and the mandible. In the pre- 

 maxillae are situated four teeth the four upper incisors. 

 Of these the two anterior are very long, curved, chisel- 

 shaped teeth, which are devoid of roots, growing throughout 

 life from persistent pulps. Enamel is present, as a thick 

 layer, on the anterior convex surface, which accounts for the 

 bevelled-off character of the distal end the layer of enamel 

 being much harder than the rest, which therefore wears away 

 more quickly at the cutting extremity of the tooth. The 

 second pair of incisors of the upper jaw are small teeth which 

 are lodged just behind the larger pair. In the lower jaw are 

 two incisors, which correspond in shape with the anterior 

 pair of the upper jaw. The remaining teeth of the upper 

 jaw are lodged in the maxillae. Canines, present in most 

 Mammals as a single tooth on each side, are here entirely 

 absent, and there is a considerable space, or diastema, as it 

 is termed, between the incisors and the teeth next in 

 order the premolars. Of these there are three in the 

 upper jaw and two in the lower. They are long, curved 

 teeth devoid of fangs, the first smaller than the others. 

 Behind the premolars are the molars, three on each side 

 both in the upper and lower jaws. The premolars and 

 molars, like the incisors, grow throughout life from persistent 

 pulp. 



Opening into the cavity of the mouth are the ducts of 

 four pairs of salivary glands. On the floor of the mouth is 

 the muscular tongue, covered with a mucous membrane 

 which is beset with many papillae. The roof of the mouth 



