STRUCTURE OF THE COATS OF THE EYEBALL. 261 



and most animals they are elliptical, and consist of a core and lamel- 

 lated sheath (see Lesson XXL). 



The lachrymal gland may be briefly mentioned in connection with 

 the eyelid. It is a compound racemose gland, yielding a watery secre- 

 tion, and resembling in structure the serous salivary glands, such as the 

 parotid. Its ducts, of which there are several, open at the upper fold 

 of the conjunctiva, near its outer extremity. 



The sclerotic coat is composed of dense fibrous tissue, the bundles 

 of which are intimately interlaced. It is thickest at the back of the 

 eyeball. It is covered externally with a lymphatic epithelium, while 

 internally it is lined by a layer of connective tissue containing pig- 

 ment-cells, which give it a brown appearance (lamina fusca). At the 

 entrance of the optic nerve the sclerotic is prolonged into the sheath 

 of that nerve, the bundles of which, piercing the coat, give a sieve-like 

 aspect to the part (lamina cribrosa, fig. 298, L). 



FIG. 290. A. CORPUSCLES OF THE RAT'S CORNEA. (From a preparation treated 

 with chloride of gold.) B. CELL-SPACES OF THE RAT'S CORNEA. (From a 

 preparation stained with nitrate of silver.) 



The cornea (fig. 289) consists of the following layers enumerated 

 from before back : 



1. A stratified epithelium continuous with the epithelium of the 

 conjunctiva (1). 



2. A thin lamina of homogeneous connective tissue (membrane of 

 Bowman), upon which the deepest cells of the epithelium rest (2). 



3. A thick layer of fibrous connective tissue which forms the proper 

 substance of the cornea (3). This is continuous laterally with the tissue 

 of the sclerotic. It is composed of bundles of white fibres arranged in 

 regular lamina?, the direction of the fibres crossing one another at right 



