370 F. L. LANDACEE 



nor directly related to the Xth, nor is it at first in contact with the 

 auditory ganglion proper, but arises separately and can be fol- 

 lowed continuously until it assumes the relations ascribed to it in 

 the adult by Herrick ('01) . At one stage in the enlargement of the 

 auditory vesicle its relations are somewhat confused on account 

 of the fact that the vesicle grows back and around the ganglion, 

 but it can be followed, as mentioned, continuously. There is a 

 later stage also where the lateralis IXth comes into contact with 

 the motor root of the IXth and before the motor root has grown 

 ventrally as far as the root of the epibranchial ganglion, when it 

 is impossible to distinguish between the lateralis cells and the 

 cells of the growing motor root. This condition is illustrated in 

 fig. 59. In this stage we have the lateralis ganglion and the motor 

 root closely combined. The constituents which can be positively 

 identified as entering into the IXth ganglion are: first, the cells 

 derived from the epibranchial placode situated in the distal por- 

 tion of the ganglionic mass in the early stage, and extracranially in 

 the latter stages: and secondly, the proximally situated lateralis 

 ganglion, derived from the posterior portion of the auditory vesicle 

 and closely associated with the motor root in its early stages, and 

 in the later stages situated intracranially. 



In discussing the differentiations of the postauditory lateral 

 mass (p. 349-50) attention was called to the appearance in one 

 series of a slight condensation of the lateral mass derivatives, in the 

 region of the IXth ganglion just posterior to the auditory vesicle. 

 This condensation appears in some series and not in others, so that 

 one cannot be positive that no cells derived from the lateral mass 

 enter into the proximal or lateralis portion of the IXth ganglion in 

 its later stages. The early stages of the lateralis IXth are quite 

 definite in origin and distinct in outline, and if lateral mass cells 

 do enter into its composition they would be homologous to the pre- 

 auditory lateral mass, and the ganglion would have a double 

 composition and would resemble the VHIth, if this ganglion con- 

 tains lateral mass cells or the lateralis Vllth, rather than the later- 

 alis Xth. The relations are difficult to unravel here, partly because 

 of the presence of the motor root and partly because the cells 



