VERTEBRATE PHOTORECEPTORS 



made to describe the histological structure of the various 

 parts of the bulb because of excellent descriptions found in 

 various textl)ooks of histology and treatises on ophthal- 

 mology. 



The Bulb 



The human eyeball (bulbus oculi) is made up of the 

 segments of two spheres, a scleral segment and a corneal 

 segment — the former having a radius of 12 mm. and the 



Cornea 



Conjunctiva 

 Canal of Schlemm 



Med. rectus 



Posterior chamber 

 Limbus 



Ciliary muscle 



Lat. rectus 



Sclera 

 Choroid 

 Retina 



Optic nerve 



Fig. 2. Schematic horizontal meridional section of the human rip;ht eye. X 3, 

 A. P., anterior pole; P.P., posterior pole; V.A., visual axis. (From Bailey. 

 Textbook of Histology, 10th Fdition, The Williams & Wilkins Company, 

 Baltimore.) 



latter a radius of 8 mm. (Figure 2). At the junction of 

 the two segments which are continuous structurally, there 

 is a shallow circular furrow known as the external scleral 

 sulcus. The anterior (corneal) segment occupies about one- 

 sixth of the surface of the bulb, which is relatively very 



