476 THE NERVE DISTRIBUTION IN THE EYE OF PECTEN IRRADIANS. 



toward the periphery of the eye. Their large granular elliptical nuclei (Figs. 2, 3, nl. 

 b'pol.) may be seen in longitudinal sections extending in a row a short distance from 

 the median limiting membrane. The whole cell with its afferent and efferent axon 

 is encased in a hyaline sheath under which are scattered blue granules of different 

 sizes. In methylen-blue sections under magnification of 2,500 diameters may be 

 seen small dendritic fibres at the end of the afferent axon in contact with the anterior 

 end of the rod-cell. Between this dendritic termination and the knob-like endings 

 of the rod-axon is a spherical mass of highly refractive protoplasm. In sections 

 stained with iron haematoxylin, the hyaline sheath does not show, and only the bipolar 

 nucleus and its axons are visible. Near the median limiting membrane, where the 

 axon terminates is seen the small rod nucleus (Fig. 3, nl. bac.) surrounded by a refrac- 

 tive elliptical capsule. Several of the efferent axons of the bipolar cells terminate 

 at the periphery in a common large ganglionic cell. 



The marginal ganglionic cells (Fig. 3, gn. marg.) not only make connections with 

 the axons of the bipolar cells but with other axons, and from them, moreover, fibres 

 extend toward the base of the eye, forming thus a hemispherical cage of fibres that 

 encloses the posterior part of the eye from the margin to the base of the retina. Here 

 they unite to form the large basal optic nerve that goes to the brain. 



The nerve-fibres of the basal optic nerve are somewhat varicose and wavy and 

 with nodular thickenings. Several of them may proceed from a marginal ganglionic 

 cell surrounded by a thin sheath and soon separate into fine fibres (Fig. 3, }br. opt. 6a.). 

 The marginal ganglionic cells are arranged in several rows around the border of the 

 median layer. Sections cut from near the margin show that each large ganglionic 

 cell contains a nucleus and several nucleoli, and that the protoplasm around the 

 nucleus is arranged in granular striations except where the bipolar cell makes con- 

 nection; here a hillock of granular neurosomes and reticular fibrillae exist (Fig. 3, gn. 

 marg.). Near the base of the eye, a side branch (Fig. 1, rm. I.) of nerve-fibres arises 

 from the large basal nerve-trunk. It proceeds in a connective-tissue sheath along one 

 side of the eye to the septal membrane. It extends along this membrane giving off 

 fibres in its path. These as well as its remaining fibres radiate to end in the external 

 ganglionic cells. 



In good methylen-blue sections the external ganglionic cells are seen to form a 

 one-layered plate of contiguous blue masses (Figs. 1, 2, 3, gn. ex.) proximal to the 

 septal membrane. They are ve^ peculiar structures, having the appearance of a 

 much entangled coil of characteristically beaded fibres, surrounded by a spheroidal 

 membrane. From each ganglionic cell many beaded fibres pass, not only to the 

 neighboring ganglionic cells, forming thus a continuous layer of nerve-tissue at the 



