560 



SIGNIFICANCE OF THE NERVOUS SYSTEM 



for example, we find enormous numbers of small and large pyramidal cells, while 

 those constituting the spinal ganglia, are spherical, and those forming the ventral 

 horn of the gray matter of the cord, rather square irregular. Very typical flask- 

 shaped cells are found in the cerebellum. Many of these cell-bodies are visible 

 to the naked eye, for example, those of the cells of Purkinje (Fig. 276) and those 

 situated in the anterior horns of the gray matter of the cord (150/x). Others, 

 again, are extremely small, measuring only from 4-9/i in diameter. 



The large pyramidal cells in the cerebral cortex (Fig. 277) measure from 20-30;u 

 and the small ones from 10-12jU in diameter. Among the smallest are those com- 

 posing the olfactory bulb, and those forming parts of the cerebellum. Neither are 

 we in a position to give definite measurements regarding the length of the neuron 

 as a whole, because the distances which the different nerve paths must cover, vary 



D " 



FIG. 276. PURKINJE CELL, FROM HUMAN CEREBELLUM. 

 Golgi's method of staining. (Siohr.) 



very greatly. It is said, however, that they may attain a length of 1.0 m., bridging 

 the distance between the motor area of the cerebrum and the lumbar region of the 

 spinal cord, or the distance between the latter and the effectors in the foot. On 

 the afferent side, they do not attain so great a length, because the sensory paths 

 are usually beset with a greater number of relay stations. It is also of interest 

 to note that the volume of the axons of these cells greatly exceeds that of the 

 cell-bodies. In large motor cells, for example, the axis cylinder plus its enveloping 

 sheath, possesses a volume 1500 times greater than that of the cell-body. Golgi 1 

 recognizes three types of cells, namely: 



Type 1. The dendrites are short and ramify in close proximity to the cell-body. 

 Broad and thick at their origin, they gradually become thinner as they divide in an 



1 Boll. d. Societa Med. Chir. di Pavia, 1898-1899. 



