460 CONJUNCTIVA AND SCLEROTIC. 



maceration, in the form of a thin lamina perforated by many 

 small holes, which is continuous with the internal surface of the 

 sclerotic. This lamina is the so-called lamina cribrosa. The 

 foramina correspond to the several fasciculi of the optic-nerve 

 fibres which traverse it. Near its centre are two close together, 

 of large size, through which the retinal vessels pass. 



The sclerotic becomes denser and more uniform in structure 

 as we pass from without inwards. Irregularly shaped flat 

 pigment cells, with clavate or radiating processes-, are deposited 

 in the very dense tissue lining its smooth inner surface, and this 

 is especially the case in dark eyes, giving to it, when they are 

 present in large numbers, a brownish aspect. 



The arrangement of the fibres of the sclerotic was first 

 described by Valentin.* Briicke was only able to support 

 his statements so far as to say that, speaking generally, there 

 were antero-posterior and circular fibres in the sclerotic, 

 forming by their decussation a dense tissue, and that the fibres 

 of the tendons of the recti muscles, after they have reached 

 the sclerotic, spread out in a fan-like manner, and, dipping 

 into the mesh- work of the sclerotic, essentially strengthen its 

 anterior portion. 



That the sclerotic fibres are composed of connective tissue 

 has already been shown at p. 79, vol. i. Cellular elements 

 resembling the corpuscles of the cornea are distributed through 

 the matrix. If a point of nitrate of silver be drawn across the 

 sclerotic of a live Rabbit, the delicate lines of the serous canals 

 may be seen in surface sections, when it is completely reduced. 

 On the other hand, preparations made with chloride of gold 

 give a positive to the negative images of the silver method. 

 I have, indeed, only seen the latter in a preparation exhibited 

 to me by Dr. Carmelt, of New York ; in this instance, how- 

 ever, they were so sharply defined that no doubt of their pre- 

 sence could exist. The cells that lie in these spaces contain, 

 in many Mammals, pigment granules. f 



In Birds the sclerotic is composed of hyaline cartilage, in- 

 vested both externally and internally by connective tissue. 



* Repertorium, Band i., Heft, iv., p. 301. 

 f Leydig, loc. cit. 



