xm 



PHYLUM CHORDATA 



445 



Lizard in being divided into two parts by a transverse muscular 

 partition, the diaphragm. The anterior part, or thorax, contains 

 the heart and the roots of the great vessels, the lungs and bronchi, 

 and the posterior 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. 



Digestive Organs. The teeth (Fig. 1093) 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 an- 

 terior are very long, 

 curved, chisel-shaped 

 teeth, which are devoid 

 of roots, growing 

 throughout life from 

 persistent pulps. 

 Enamel is present, and 

 forms a thick layer on 

 the anterior convex sur- 

 face, which accounts 

 for the bevelled-off 

 character of the distal 

 e n d t he layer of 

 enamel being much 

 harder than the rest, 

 which therefore wears 

 more quickly away at 



J cb 



inc 



rtcis.pa.1 



FIG. 1098. Lepus cuniculus. Vertical section through 

 the anterior part of the nasal region of the head. inc. 

 section of larger incisor tooth ; jcb. lumen of Jacobson's 

 organ, surrounded by cartilage ; Icr. dct. lacrymal duct ; 

 max. maxilla ; max. trb. maxillary turbinals ; nas. nasal 

 bone ; nas. pal. naso-palatine canal ; sept. cart, carti- 

 laginous nasal septum. (After Krause.) 



re tj uujjiiy awaj fctu 



the cutting extremity 

 of the tooth. Along 

 the anterior surface is a 

 longitudinal groove. 

 The 'second pair of in- 

 cisors 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* main difference consisting in the absence 

 of the longitudinal groove. The remaining teeth of the upper jaw 

 are lodged in the maxillae. Canines, present in most Mammals as a 

 single tooth on each side, above and below, 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 

 pre-molars. Of these there are three in the upper jaw and two in 

 the lower. They are long, curved teeth with persistent pulps like 

 the incisors. The first of the upper jaw is smaller than the others 



