MOTOR NUCLEI IN PHYLOGENY 79 



glossal nucleus) are thus distributed in their exit over a relatively 

 wide area to three roots, viz., 'a,,' 'h,' and 'c' of Fiirbringer. 



In one respect, viz., in its more rostral position in the brain 

 stem, the hypoglossal nucleus of reptiles shows a marked advance 

 over the condition obtaining in Amphibia. This fact is well 

 known from Kappers' earlier investigations (1. c.) and may be 

 clearly demonstrated by reference to figures 11 and 12, where 

 it will be seen that the hypoglossal nucleus extends to within a 

 relatively short distance of the rostral end of the motor X column 

 and a condition obtains which foreshadows the more complicated 

 relations characteristic of birds and mammals. 



From these reconstruction charts it is evident that the distance 

 between the caudal border of the motor VII root and the rostral 

 end of the cervical motor column is much less in reptiles than 

 in amphibians, and further that with regard to the character in 

 question there is a remarkable degree of uniformity among the 

 reptiles examined. That the marked difference of this measure- 

 ment in reptiles and amphibians is not due to the persistence 

 in the former animals of the motor roots of the rostral occipito- 

 spinal nerves is further evident on comparing such forms as 

 Chelone and Triton, in both of which the full number of these 

 roots persist (Furbringer, 1. c). 



With regard to the influences which have contributed to the 

 rostral migration of the XII nucleus in reptiles, the following 

 facts are significant. In reptiles as in adult amphibians the 

 distribution of gustatory sense organs is limited to the buccal 

 and pharyngeal regions (Kappers, 33). In contrast to amphi- 

 bians, however, the mucosa covering the rostral portion of the 

 tongue is innervated by trigeminal fibers in reptiles, among whom 

 for the first time in phylogeny the lingual branch of the trigeminal 

 nerve appears (Kallius, 29, p. 748). 



The nucleus of termination for the V lingual fibers is chiefly in 

 the dorsal area of the substantia gelatinosa Rolandi, as Van 

 Valkenburg has shown (40). This author has pointed out that 

 the descending fibers of the mandibular division of the trigeminal 

 root do not extend so far caudad as do those of the ophthalmic 

 and maxillary roots, and further that the position and entity 



