NERVUS TERMINALIS : MAMMALS 37 



by naked threads. In some cases these naked filaments repre- 

 sent fibers which have lost their myelin sheaths (fig. 8A, ax. 

 cyl.). Many of them show very large varicosities (fig. 8, A and 

 B), the most pronounced of which are often found near the 

 nodes of Ranvier. These varicosities appear to have been pro- 

 duced by unequal shrinkage of the axis cylinder, probably dur- 

 ing the process of fixation of the tissue. At other points, as 

 «ho^\Ti in the figures, the cylinders are extremely attenuated. 

 Some show spiral formations of the axis cylinder within the 

 myelin sheath (fig. 8A, sp.). In diameter the intracranial 

 myelinated fibers varied from 1.5 m to 2.6 /x. 



In the septal plexus of the terminalis, myelinated fibers are 

 found intermingled with the unmyelinated threads (fig. 22). 

 As previously stated, these belong, in part at least, to the tri- 

 geminus. It is possible that the myelinated fibers of the intra- 

 cranial plexus are related to those found in the septal plexus, 

 and may therefore be trigeminal in origin. This does not seem 

 likely, but can only be adequately tested by degeneration experi- 

 ments, which the writer hopes ^o perform. 



The roots which enter the brain, in both of the extra-uterine 

 stages of growth of the cat in which this point was examined, 

 appear to be composed exclusively of unmyelinated threads (fig. 

 23). Fibers of Remak predominate, but a few naked filaments 

 are mingled with them. 



Nerve terminations. There are present in the cat two kinds of 

 nerve terminations in the walls of the cerebral blood-vessels, 

 which are connected with fibers from the nervus terminalis. 

 A third type consisting of free endings in the epithelium of the 

 nasal septum appears also to be related to this nerve. 



The nerve terminations in the walls of the anterior cerebral 

 artery and its branches, for convenience of description, will be 

 designated as type I and type II. 



Type I (figs. 24 to 27) consists of delicate varicosed fibers 

 which penetrate the muscular walls of the >blood-vessels from the 

 nervous plexus surrounding these vessels.^ At varying depths 

 in the muscular layer, the fibers which penetrate the arterial coat 

 ramify into very fine arborizations which pass between the sniooth 



