138 Mr. Hulke on the Minute Anatomy of the Retina. [Feb. 18, 



February IS, 1864. 



Major-General SABINE, President, in the Chair. 



The following communications were read : — 



I. "A Contribution to the Minute Anatomy of the Retina of Amphibia 

 and Reptiles." By J. W. Hulke, Esq., F.R.C.S., Assistant- 

 Surgeon to the Middlesex and the Royal London Ophthalmic 

 Hospitals. Communicated by W. Bowman, Esq. Received 

 February 4, 1864. 



(Abstract.) 



The animals of which the retina was examined were the frog, the black 

 and yellow salamander, the edible turtle, the water- and the land-tortoise, 

 the Spanish Gecko, the blindworm, and the common snake. The method 

 adopted was to examine the retina (where possible) immediately after 

 decapitation of the animal, alone and with chemical agents ; and to make 

 sections of the retina hardened in alcohol or in an aqueous solution of 

 chromic acid, staining them with iodine or carmine, and adding glycerine, 

 pure and diluted, to make them transparent. The following is a summary 

 of the results of the examination. 



1 . The rods and cones consist of two segments, the union of which is 

 marked by a bright transverse line. 



2. Each segment consists of a membrancus sheath and contents. 



I J 3. The outer segment, or shaft, is a long narrow rectangle (by inference, 

 a prism or cylinder). It refracts more highly than the inner segment. Its 

 contents are structureless, and of an albuminous nature. It is that part 

 which is commonly known as " the rod.'' It is smaller in the cones than 

 in the rods, and in the cones narrows slightly outwards. 



4. The outer ends of the shafts rest upon the inner surface of the 

 choroid, and their sides are separated by pigmented processes, prolonged 

 from the inner surface of the choroid between them to the line that marks 

 the union of the shaft with the inner segment. The effect of this is that 

 the shafts are completely insulated, and rays entering one shaft are pre- 

 vented passing out of it into neighbouring shafts. 



5. The inner segment of the rods and cones, or body (the appendage of 

 some microscopists), has a generally flask-shaped form, longer and more 

 tapering in the rods, shorter and stouter in the cones. It is much paler 

 and less conspicuous than the shaft. It fits in an aperture in the membrana 

 limitans externa. 



Its inner end always encloses, or is connected by an intermediate band 

 with an outer granule which lies in or below the level of the membrana 

 limitans externa. Its outer end, in cones only, contains a spherical bead 

 nearly colourless in the frog and blindworm, brilliantly coloured in the 

 turtle and water- and land- tortoises, and absent from the common snake and 

 Spanish Gecko. In addition to this bead, where present, and the outer gra- 



