24 'Journal of Cotnparativc Neurology and Psychology. 



mandible. The buds of the middle of the lip cannot be separated 

 from buds of the lateral portion of the lip even in the earlier 

 stages, although innervated separately by the internal and exter- 

 nal branches, respectively, of the ramus mand. V. They would 

 undoubtedly function as a unit. 



If we compare the posterior limit of the dorsal lip and breathing 

 valve group (Table V) with the anterior limit of the lower lip and 

 mandible group (Table VI), it will be seen that there is no over- 

 lap. The posterior limit of the former group for series K', L, 

 M and N are sections 15, 16, 20 and 21, respectively, and the 

 anterior limit of the latter group for series L, M and N are 20, 30 

 and 27, respectively. The ventral group underlies the dorsal in 

 later series, however, and its failure to do so in. the earlier series 

 is due probably to the elongation of the upper parts of the head 

 on account of the rapid growth of the brain. This is equalized 

 later by the growth of the lower jaw to fit into the upper. 



The posterior limit of buds on the mucosa of the mandible 

 moves backward, as stated above, until in series N it comes to 

 the region occupied by the most anterior buds of the anterior pal- 

 atine group, and in series O' reaches the anterior buds of the 

 mid-ventral pharyngeal group which, however, had appeared first 

 in an earlier series (N). 



The spreading of the buds back from the anterior portion of the 

 mandible both on the mucosa and on the skin, as will be shown 

 presently, toward the posterior or proximal portion and the man- 

 ner in which the nerve runs along the mandible from the proxi- 

 mal toward the distal portion is conclusive evidence that in these 

 two cases the more peripheral buds supplied by these nerves 

 receive fibers before the proximal buds do. 



The functional need of the organism, represented by the more 

 or less continuous spreading of the buds from the lips out over 

 the surface of the body and back in the oral cavities, seems to 

 furnish the key to the explanation of the methods of spreading 

 rather than the anatomical arrangement of the nerves. Buds 

 rarely or never in the oral and cutaneous groups appear on the 

 shortest twigs or the proximal distribution of a nerve first, but 

 always on the distal or longest portions, since this maintains the 

 continuity in the anterior-posterior method of spreading. 



(b) Buds lying on the skin of the mandible outside the mouth, 

 and on the mental and post-mental barbules (groups B, C and D). 



