352 F. L. LAND ACRE 



situated low in the body on a level with the dorsal portion of the 

 gill slit and is connected with the medulla by the narrow strand of 

 loose cells described above. The outline of the ganglion is still 

 indefinite and its ventral portion is closely applied to the meso- 

 derm underlying it. All of the visceral portion of the Xth except 

 that derived from the placodes seems to come from the ventral 

 portion of the lateral mass, while the jugular or general cutaneous - 

 ganglion comes from the dorsal portion. The jugular ganglion 

 cannot be detected for some time after the visceral Xth is formed. 

 Owing to the intimate relation of the lateral mass portion of the 

 Xth ganglion to the epibranchial placodes, it will be better to 

 describe the lateralis Xth first and return to the visceral Xth later 

 (p. 79). The fate of the lateral mass cells in the region of the IX 

 ganglion will be taken up with the lateralis IXth. The relation 

 of the visceral Xth ganglion to the jugular or general cutaneous 

 Xth which appears later and is situated near the medulla intra- 

 cranial^, is extremely interesting. It will be recalled that the 

 lateral mass anterior to the ear gives rise to the Gasserian, a pure 

 cutaneous ganglion, and to a part of the geniculate, a visceral 

 ganglion which fuses with the ganglion from the epibranchial 

 placode. Both these ganglia become closely fused in the adult 

 and are situated intra-cranially. In the Xth, however, we have a 

 complete separation of the general cutaneous and visceral portions; 

 the former being small and situated intra-cranially, the latter 

 large and situated extra-cranially and fusing with the placodal 

 ganglion just as the geniculate does. From evidence to be brought 

 out later it appears that the lateral mass contingent of the gen- 

 iculate and visceral Xth is really a general visceral component, 

 the special visceral or gustatory ganglia being derived from the 

 placodes. In types having a well defined neural crest these same 

 relations would seem to hold, i.e., the general cutaneous and general 

 visceral ganglia of the head have a common derivation from the 

 neural crest, which is homologous with the neural crest of the spinal 

 cord. The chief difference between the brain and the cord in this 

 respect lies in the greater size of the cranial ganglia and the ex- 

 tent to which the general cutaneous component and general vis- 

 ceral component, which are both represented in the spinal ganglia, 



