The Afferent and Efferent Neurons 



73 



chiasm {chiasma optictem), [Fig. 67], where the fibers for the right half 

 of each retina pass to the right optic tract, and the fibers for the left half 

 to the left optic tract. In each optic tract some of the axons run to the 

 external geniculate body (corpus geniculatum laterale), [Fig. 69], 

 and some to the internal geniculate body (corp. gen. mediate), on 



Fig. 6i. Schematic representation of the sensory apparatus in the retina of the 

 human eye. (Merkle-Henle, Anatomie.) I, Layer of pigment cells next to the cho- 

 roid. 2, Processes of the pigment cells. 3, Rods. 4, Bodies of rod-cells. 5, Cones. 

 6, Axons of cone cells. 7, Cone-bipolar cells. 8, 9, Ganglion cells. 10, Optic nerve 

 fibers (axons of ganglion cells), u, 12, Horizontal cells. 13, 14, 15, 16, Cells of dif- 

 ferent types; functions unknown. 17, Fibers (axons probably) of cells having bodies 

 in the brain. 18, Neuroglia cells. 19, Radial fiber (Miiller's fiber; part of the susten- 

 tacular syncytial framework of modified neuroglia). 



the same side, arborizing there in contact with interconnecting neurons, 

 whose fibers continue in the optic tract to the ' occipital lobes ' of the 

 cerebral cortex, or run to other ganglia in the mid-brain. 



THE EFFERENT NEURONS. 



The efferent neurons of the spinal system have their cell bodies in the 

 gray matter of the cord, the axons leaving the cord on the anterior side 

 (forming therefore the anterior roots), and joining the fibers of the 

 ' posterior roots ' to make the complete spinal nerve just beyond the 



