MOTOR NUCLEI JN PHYLOGENY 383 



labelled Nu.XII (hypoglossal nucleus) and the rootlet arising 

 from it is labelled R.XII (hypoglossal root), while in figure 1 

 the corresponding rootlets are labelled simply R.sp. 2 m. (motor 

 root of second spinal nerve), since at this level they have their 

 origin in both dorso-medial and ventro-lateral areas. 



A similar arrangement ot cell groups obtains in Rana escu- 

 lenta (Kappers) and in Bufo (Rothig), though these authors 

 have not indicated the extent ot the dorso-medial cell group in 

 their reconstruction charts as I have done in Rana catesbeana 

 (cf . fig. 9) . The relations of the cell groups described above are 

 essentially similar in the brain stem of Rana pipiens, of which I 

 have recently examined several series stained by different 

 methods. 



The arrangement of the elements in the rostral end of the 

 somatic motor column of the cord in urodele amphibians pre- 

 sents a marked contrast to the conditions obtaining in this re- 

 gion in Bufo and Rana. In adult urodeles the motor roots of 

 the first spinal nerve (first occipito-spinal) are regularly repre- 

 sented (Fiirbringer, I.e.) and the rostral end of the cervical 

 motor column shows but slight, if any signs of differentiation 

 from the more caudal segments of this region (cf. Kappers, 35 

 and Kingsbury, 40). 



Nerves IX and X 



In describing the IX-X complex m late larval stages of frogs, 

 Strong has distinguished five roots (53), A motor component 

 was lacking in the first of these roots (most rostral). The second 

 and third roots were attached very close together and some- 

 times an intermediate rootlet could be distinguished. Motor 

 components were present in both these roots but in addition to 

 the visceral sensory fibers, Strong identified a well marked gen- 

 eral cutaneous component in the third root. The fourth root 

 was separated from the third by a considerable interval and con- 

 tained but two components, viz., visceral sensory and motor. 

 The fifth and last root emerged some distance caudal to the fourth 

 and ''seems to derive its fibers from one source only" (1. c, p. 

 137). Strong considered this root to be purely motor in character. 



