ill, '-!,.. AN8 OF Till INM I: Q] ttM L ' 305 



although fr< e from papilla-, is richly pro\ idcd with follicular L'l 

 1 1 is developed out of t\\o ridg s in th- region where the second an- 1 

 third visceial arches conic together in the median plane. The 

 anterior and po.Mrior fundaments unite in a Y.-hapi-d furrow, 

 the arms of wliich diverge- in front. The circum\ allate papillae are 

 formed on the body of the tongue along this furn.w. wliich p< i 

 for a long time. Win-re the two arms of the V meet there is a d< -p 

 pit, the foramen coecum, which His ha- hrought into connection with 

 the origin of the thyroid glands, which will soon be discussed. 



(2) The Salivary Glands are demonstrable* even in the second 

 month. The fundament of the submaxillary appears first in human 

 embryos at the sixth week 



(('HIKVITZ), afterwards the 

 parotid in the eighth week, 

 and finally the sublingual. 



(3) From a morphological 

 point of view, the Teeth can 

 well he de.Mgnated as the most 

 interesting structures of the 

 oral cavity. Their develop- 

 ment in Man and Manmjals 

 is accomplished in a manner 

 Which is n,i,l,e, shnple nor 



easily intelligible ; in the " Menschliche Emlm 



lower Vertebrates, on the con- 

 trary, it is simpler, and for that reason I shall mak 

 as the starting-point of the description. 



The teeth, wliich in Mammals are attached to the edges of the 

 and only bound the entrance to the alimentary tube, possess in the 

 lower Vertebrates a very wide distribution. For in many species they 

 not only cover the roof and the floor of the oral cavity and the inner 

 Mil-face of the branchial aivlu s in imiiien>e nuinbei s. as palatal, 

 lingual, and pharyngeal teeth, but the . . di>t rilniied in cWe-set 



rows over the whole surface of the skin, and p : tf in the 



N-lachiai ig and at the same time flexible coat of mail. 



The teeth are ori>/in(ill// iwtlt* <m ossified pafnlltr <>/ the skin 



and the /// nitn-mn'. upon tiie <-ontiguou> MM ni,-h thev 



are formed. The tlrirhijmtrnt <>f the dermal teeth in Selachians shows 

 this in a very convincing ma; 



In young Shark embryos, by a prolifeiation on the part of the sub- 

 epithelial cells, there are developed on the otherwise smooth surface 



20 



