THE CRANIAL GANGLIA IN AMEIURUS 381 



present. The ganglion cells then surround the proximal part of 

 the root as indicated in fig. 76, which is taken through the middle 

 of the root and is not exactly transverse to the long axis of the 

 embryo, so that nearly the whole length of the fibrous root shows. 

 The cells occupying the proximal portion of the root where the 

 definitive jugular ganglion appears surround the root, lying an- 

 terior and posterior to it. 



There is little difference in size between the cells which occupy 

 the position in which the ganglion is later found and those cells 

 surrounding the future root. This condition persists for some 

 time, but in an embryo of 113 hours there is a decided increase 

 in the number and a change in the appearance of the cells as 

 shown in fig. 77, which is taken through the middle of the root. 

 Anterior and posterior to this point the cells are usually grouped 

 on either side of the fibrous portion of the root. 



A much later stage (fig. 78) from an embryo of 138 hours shows 

 this ganglion after it has become a prominent portion of the vagus 

 complex. The manner in which the ganglion cells are distributed 

 through the root and their small size explains the difficulty one 

 finds in separating the cells of the future ganglion from the spindle 

 shaped cells of the root. The extra-cranial portion of the lateral 

 mass I shall not describe further in detail. It is so large and in- 

 creases in size so rapidly that it is by far the most conspicuous 

 structure in this region of the body. It is too large, in fact, to 

 draw under a camera at the same magnification I have used for 

 the other portions of the ganglia. The figures (72 and 73) show 

 it in the early stages and figs. 79, 80, 81 and 82 show its relative, 

 size and relations. There is never any difficulty in locating the 

 bulk of this ganglion after the 81st hour. There is the difficulty of 

 determining its dorsal boundary, mentioned above, since it extends 

 as a thin mass of cells dorsally to join the jugular. Its separation 

 from the jugular is in all but these early stages, quite distinct. 



The fact that this lateral mass ganglion consists of two parts, 

 an intra-cranial which is general cutaneous, and an extra-cranial 

 which is visceral supplying visceral surfaces, has an interesting 

 bearing on the relation of spinal and cranial nerves. 



