Landacre, Taste Buds of Ame'iurus. 39 



body between the third and fourth lateral line organs in a pos- 

 terior direction can only be interpreted as a spreading from 

 the proximal toward the distal distribution of the nerves, since 

 the nerves arise anterior to the areas innervated. This it will 

 be recalled is in sharp contrast with the condition usually found 

 in the areas lying anterior to the origin of the nerves. 



The location of the cutaneous groups is shown in text figures 

 I to 4, p. 1^-]. 



9. THE ANTERIOR PALATINE GROUP. 



This group consists of buds lying on the anterior roof of the 

 mouth. It has quite definite boundaries structurally and its 

 mucous membrane is quite sharply differentiated anteriorly 

 from that of the lip and breathing valve. The lip and breath- 

 ing valve have a thick mucous membrane, while that of the 

 palate is quite thin as late as series U (244 hours), so that the 

 separation of these groups is quite easy, without considering the 

 area devoid of buds between them, and the difference in time 

 of appearance. In the 20| mm. embryo, however, the mucous 

 membrane of the anterior roof of the mouth is quite as thick 

 as that of the breathing valve, but usually stains lighter. Even 

 if this histological difference were not present, it would be quite 

 easy to determine the anterior boundaries of this group, since 

 the breathing valve always has a free border posteriorly and 

 medially and there is, as mentioned above, no continuity in the 

 distribution of buds from the valve to the palate. 



This group is supplied exclusively by the ramus palatinus 

 VII, while the following group is supplied by the ramus pala- 

 tinus posterior. The posterior boundaries of the anterior palatine 

 group are not so definite as the anterior boundaries but there is 

 always in the earlier series and even up to series U (244 hours), 

 a well defined area devoid of buds between the anterior and pos- 

 terior palatine groups. 



This group appears first in series N (138 hours), when four 

 buds are found arranged symmetrically on either side of the me- 

 dian line. In fact, this whole group up to the time when there 

 are 20 buds present in U is entirely symmetrical, the same num- 

 ber of buds lying on either side of the median line. Up to series 

 R (183 hours), there are only four buds. From this time on 



