354 



NORMAL HISTOLOGY. 



with the nerve-fibres composing the central nervous system. The entire 

 nerve corresponds to a huge funiculus, the perineurium being represented 



Blood-vessel 



i ^<. 'V 



/ ' 



" . . .-'; -, 

 .'-.- './ ~ , '. 



' . - v 



Interfascicular /_ . . . 



on nective tissue ~~q~ * r T~- * ~~~ - ' '' .* 



^1 



I 

 FIG. 404. Transverse section of part of optic nerve, showing bundles of nerve-fibres. X 125. 



by the pial sheath, and the endoneurium by the interfascicular septa of con- 

 nective tissue prolonged from the pia between the bundles of fibres. Nu- 

 merous connective tissue cells occur along the strands of fibrous tissue. 



THE CRYSTALLINE LENS. 



The lens, the most important part of the refractive apparatus of the eye, 

 is a biconvex body suspended from the ciliary body by the suspensory liga- 

 ment or zonule of Zinn. Its anterior surface supports the pupillary margin 

 of the iris, its posterior surface resting in a depression, the patellar fossa, on 

 the anterior surface of the vitreous body. It is completely transparent and 



enclosed in a transparent elastic 

 membrane, the lens capsule. Togeth- 

 er with the capsule, the lens measures 

 from 8-9 mm. in its transverse 

 diameter, and about 4 mm. in thick- 

 ness from pole to pole. 



The capsule, which entirely 

 surrounds the lens, is a transparent, 

 structureless, highly elastic mem- 

 brane, which, while resistent to 

 chemical reagents, cuts easily and 

 then rolls outwards. It is thickest 

 on the anterior surface, where it 

 measures from 10-15 /-*, and thinnest 

 at the posterior pole (5-7 /t). In the 

 adult the lens is devoid of blood- 

 vessels, but during a part of fcetal 

 life it is surrounded by a vascular network, the tunica vasculosa lentis, which 

 is supplied chiefly by the hyaloid artery. This temporary vessel is the ter- 

 minal branch of the central artery of the retina and passes from the optic 

 disk forwards through the hyaloid canal or canal of Cloquet in the vitreous to 

 the surface of the lens (Fig. 383). The vascular lens-tunic and the hyaloid 



FIG. 405. Fibres of crystalline lens ; A, B, frag- 

 ments of isolated fibres ; C, fibres in cross-section. 



X275- 



