MOTOR NUCLEI IN PHYLOGENY 85 



In all reptiles in which it occurs, the R. accessorius X is formed 

 by the union of the most caudal roots of the vagus series. Thus, 

 in reptiles as in fishes (4) and amphibians (5) the central origin 

 of the homologue of the accessory nerve of mammals must be 

 represented by the caudal end of the motor vagus column. 



In the earlier discussion of the homologues of the accessory 

 nerve in ichthyopsidans (5, pp. 415-420) it was pointed out that 

 the two elements (somatic and visceral) -of the trapezius complex 

 of higher forms might well be represented as discrete effectors 

 in lower forms, but that a primitive prostadium of the typical 

 sauropsidan condition might be looked for among the more 

 generalized amphibians. Apparently such conditions obtain 

 respectively among anurans in Rana and among urodeles in 

 Siren. 



At the time when the discussion alluded to above was published, 

 I was under the impression then current that among reptiles, 

 snakes alone were devoid of any vestige Of a nerve homologous 

 with the ramus accessorius vagi of mammals. The exact investi- 

 gations of Willard have, however, brought to light the fact that 

 in a saurian such as Anolis, which presents no very highly special- 

 ized features, the visceral component of the trapezius complex 

 is entirely absent. 



The somatic components of the muscular complex are well 

 represented in Anolis where the m. episterno-cleido-mastoideus 

 and m. capiti-dorso-clavicularis are, save in respect to their 

 nerve supply, essentially similar in their relations and functions 

 to the similarly named muscles of Hatteria and many of the 

 Lacertae, to the m. capiti-sternalis and m. dorso-scapularis of 

 the Chamaeleonidae, to the m. capiti-sternalis and m. dorso- 

 scapularis of crocodiles and to the m. capiti-plastralis of chelon- 

 ians (Fiirbringer, 16 and 17). 



Until recently it has naturally been supposed that the absence 

 of the accessorius nucleus in snakes was a condition acquired 

 subsequently to and consequent upon the loss of their shoulder- 

 girdle and its visceral levator musculature. In the light of 

 Willard 's findings, the foregoing conception may require modi- 

 fication, for it is at least possible that in the forms ancestral to 



