13FS 

 and flhich Retzias ('93), and Vsritti ('97) have iesi^natel aft-r 

 the naras of ths discoverar. Cajal neurones have been observed 

 in all of the higher vertebrates by various investigators, and 

 their identification in the brain of Mustelus makes it prob- 

 able that they are common to all groups. 



A Cajal neurone is dra«n in Pig. 41. This neurone occu- 

 pies a superficial position, just beneath the stratum of fi- 

 bres noted above; refer to Pig. 31. The cell-body is an irreg- 

 ularly elongate-oval, with its major axis horizontal. Prom its 

 opposite extremities, thick dendrites arise which run more or 

 less nearly parallel with the limitans externa. A dendrite 

 does not have marked turns in its coarse. It gives off branch- 

 es along its upper margin which ascend toward the surface of 

 the brain, while a few branches are derived from its under side 

 and penetrate to deeper levels. The dendritic surface bears 

 small gemmules and larger bosses in considerable numbers. 



The axone is a direct continuation of one of the dendrites. 

 Its point of origin is indicated by the surface becoming smooth 

 and the course more irregular. The axone continues to hold a 

 course tangential to the limitans externa, and it terminates 

 through a few small branches at no great distance from its 

 point of origin. This type of neurone is evidently purely 

 associative, linking together areas not widely separated. 



Strict irally, the Cajal neurone is somewhat peculiar (Fig. 

 69). The tigroid substance is collectei into a few lumps of 

 relatively large size. These are disposed irregularly in the 



