594 



are seen in the acusticum in Figs. 5, 6, 7, and in the dorso-anterior 

 end of the valvula in Fig. 11. It will be noticed that in the eases 

 figured the smooth dendrites are so situated as not to enter the 

 molecular layer. In the case of the acusticum cells, those dendrites 

 which ramify in the substance of the acusticum itself do not present 

 the characteristic roughness, while those which enter the cerebellar 

 crest do show it. Moreover, it is almost always true that only that 

 part of a given dendrite which is actually surrounded by the fine 

 fibres of the molecular layer is supplied with the short spines. In the 

 case of the cell shown in Fig. 11, those dendrites which have the 

 characteristic roughness are surrounded by these fine fibres, while 

 those which appear strongly varicose or moniliform are in contact 

 with the coarse, varicose fibres of the Tractus lobo-cerebellares. There 

 are many such cells in this part of the cerebellum. In addition to 

 these facts may be mentioned the occurrence of cells of the II type 

 with dendrites having the roughness characteristic of the Purkinje 

 cell dendrites. These cells, too, are situated among the fine fibres of 

 the molecular layer, and it is true that all those cells of the II type 

 which are situated thus are provided in greater or less degree with 

 such dendrites. These facts suggest that the peculiar dendrites in 

 question owe their form to the fact that they receive stimuli from 

 the enormous number of extremely fine fibres among which they lie. 

 A similar relation exists, I think, between the character of the 

 dendrites and the fibres which stimulate them in other parts of the 

 brain. 



C. The Cranial Nerves. 



I have done no work on the distribution of the cranial nerves in 

 Acipenser, but from the descriptions given by Stannius ('49) and 

 GORONOWiTSCH we may identify the chief rami with certainty, and 

 from the work of various authors (see below) on fishes we may be 

 reasonably sure of the structures innervated by each ramus. The 

 following paragraphs contain the conclusions which seem to me to 

 follow from a study of the literature on the cranial nerves, in the 

 light of my work on the central system. The detailed examination of 

 the literature will appear in my final paper. 



The Trigeminus nerve arises by two roots (Fig. 8), a dorsal root 

 from tuberculum acusticum and spinal Vth. tract, which supplies the 

 skin in front of the eye, around the nasal pit, on the snout, and on 

 the lower jaw; and a ventral root which innervates the jaw muscles. 

 (Stannius, first root, Goronowitsch, esp. Fig. 82, blue, Ewart '89, 

 PiNKus '94, Allis '89 and '97, Strong '95.) 



