50 'Journal of Comparative Neurology and Psychology. 



to the gill arches but does not acquire buds until in series 0% 

 which is much later than the time at which buds first appear 

 on the gills, and corresponds in time with their appearance on 

 the fourth gill arch. 



In discussing the posterior palatine division it was suggested 

 that possibly that group belonged, at least functionally, with 

 the pharyngeal group, since its position corresponded in the longi- 

 tudinal axis to the anterior gill buds. If now we compare the 

 position of the posterior palatine group, and of the proximal and 

 distal hyoid groups, and the mid-ventral group, we find the fol- 

 lowing relations as indicated in Table XVI, where the areas 

 covered by these groups are given in sections. The anterior 

 and posterior sections of each group marking its boundaries. 



TABLE XVI. 

 Table showing extent of the anterior palatine, posterior palatine, proximal and distal hyoid, and 

 mid-ventral floor group of the pharynx. 



The distal hyoid group fits in with the proximal hyoid group, 

 the anterior and posterior palatine and the mid-ventral group, 

 to form a structurally homogeneous group of buds on the roof, 

 floor and sides of the area in which the hyoid lies. 



The relations are somewhat different in series O', P and Q, 

 where the posterior palatine and proximal hyoid buds have not 

 yet appeared, from that in series R, S, T and U, where those 

 groups are present and serve to cover the roof, floor and sides 

 of the pharynx completely. The condition of the buds in U w^ill 

 serve to explain these relations most easily. 



In U the posterior palatine group extends from section no to 

 170; the distal hvoid group from 103 to 151 and the proximal 

 hyoid from 152 to 174, making the whole extent of the hyoid 

 group from 103 to 174, which corresponds quite closely with 



