STKUCTUKE OF THE SKULL. 



55 



the Mammals are the only animals that have teeth im- 

 planted by two or more roots or fangs. 



The teeth are not regarded as a part of the true skeleton, 

 being developments from the mucous membrane, which is 



FIG. 62. 



an 



Skull of a Dog ; longitudinal and vertical section, with the right half of the mandible 

 or lower jaw and byoid arch the lower jaw displaced downwards to show its whole 

 form. Reduced in size. 



an, anterior narial aperture; MT, maxillo-turbinal bone; ET, ethmo-turbinal; Na, 

 nasal; ME, ossified portion of the mesethmoid; CE, cribriform plate of the ethmo- 

 turbinal; Fr, frontal; Pa, parietal; IP, interparietal; SO, supraoccipital ; ExO, exoc- 

 cipital; BO, basioccipital; Per, periotic; BS, basisphenoid; Ft, pterygoid; AS, ali- 

 sphenoid; OS, orbitosphenoid ; PS, presphenoid; P/, palatine; Vo, vomer; Mz, max- 

 illa; PM>, premaxilla; (s/i, stylohyal; eh, epihyal; ck, ceratohyal; 6ft, basihyal ; tk, 

 thyrohyal; ) = the right half of the hyoidean apparatus; s, symphysis of the mandible; 

 cp, coronoid process; cd, condyle; a, angle; id, inferior dental canal; *, the part of 

 the cranium to which the condyle is articulated. 



fundamentally the same as the external integument of the 

 body, and continuous with it. The teeth of the Mammals 

 are confined to the lower jaw and to the premaxillary and 

 maxillary bones above (Figs. 61, 62, 63). Some kinds of 



