STRUCTURE AND FUNCTIONS OF THE CEREBRUM 175 



processes, signifying rich synaptic connections. Many of these 

 neurons appear to be confined altogether within the cortex; others 

 give off myelinated axons into the underlying white matter. Inter- 

 spersed with these small cell-bodies are others which are much 

 larger, which are pyramidal in shape, and which always give off a 

 large axon into the white matter. From their shape and size 

 these are known as large pyramidal cells. In a certain region of the 

 cortex, known as the motor area, the pyramidal cells are relatively 

 gigantic, being just at the limit of naked eye visibility. 



FIG. 66. Diagram of the projection fibers of the cerebrum (from Starr). B, 

 motor (pyramidal) tract; C, body-sense tract; D, visual tract; E, auditory tract; 

 F, G and H, upper, middle and lower peduncles of cerebellum; K, decussation of 

 pyramids. Numerals refer to cranial nerves. 



The White Matter of the Cerebrum. This consists of myelin- 

 ated axons classified according to their course and distribution 

 into three groups. The so-called projection fibers (Fig. 66) are the 

 axons by which the cortex is brought into connection with the 

 other parts of the nervous system. These include afferent projec- 

 tion fibers, which are the continuations within the cerebrum of the 

 various sensory paths described in previous paragraphs (see 

 p. 172), and efferent projection fibers, which convey impulses from 

 the cortex to the rest of the Body. 



