$3% THE SCLEROTIC. [sect. 224. 



posterior circumference of the eye, where it is directly connected 

 with the sheath of the optic nerve, and becomes gradually thinner 

 as it advances forwards, becoming, however, again stronger at its 

 anterior part, where it receives the insertion of the straight muscles 

 of the eye ; hence it is continued uninterruptedly into the cornea. 

 The sclerotic yields ordinary gelatine on boiling, and consists of 

 true connective tissue, whose fibrils come out very distinctly, both 

 when teased out, and also when transverse sections are treated with 

 acetic acid. The bundles of this tissue are straighter, but other- 

 wise are intimately connected together as in tendons, and they are 

 united to form largish flat bands of various thickness, which run 

 alternately in a longitudinal and in a transverse direction in the 

 entire thickness of the coat, so that a lamellated structure is ex- 

 hibited on perpendicular sections. True independent lamina?, 

 however, are nowhere present, the different longitudinal layers, as 

 well as the transverse ones, being variously united with each other. 

 It is only on the two surfaces of the sclerotic, but especially on the 

 inner, that the longitudinal fibres collect to form somewhat thicker 

 plates, and thus receive greater independence. 



Through the midst of the connective tissue of the sclerotic, there 

 run a great number of fine elastic elements, which have the 

 same form as in tendons and ligaments (see § 80), viz., a network 

 of fibres of various degrees of fineness, in which the places 

 where the primitive formative cells were situated are indicated by 

 thickenings with rudiments of nuclei, so that the whole often 

 bears a close resemblance to anastomosing, fusiform and stellate 

 cells. During life, the elementary fibres of this network appear 

 sometimes to possess cavities with fluid contents, at least, in dried 

 sections of the sclerotic, air is seen in the bodies of all the cells, 

 giving rise to the appearance know r n as the ' cretaceous corpuscles ' 

 of Huschke. Virchoio's view, according to which these cavities are 

 a kind of nutrient canals, may, accordingly, be considered as fully 

 warranted, especially as the vessels of the sclerotic are always very 

 scanty. These vessels arise chiefly from the ciliary arteries and 

 from those of the muscles of the eye-ball, and, as Brv.che and 

 myself have found, they form a tolerably wide-meshed network of 

 capillaries of the last order. I have not yet seen any nerves in the 

 sclerotic, as described by some; the appearance of nerves in it 

 probably results from branches running on its inner side to the 

 ciliary ligament. 



The cornea is perfectly transparent, denser, and more difficult to 

 tear than the sclerotic, and is composed of three special layers : 



