PROTECTIVE MECHANISMS OF THE EYEBALL 103 



produced in this case he infers, as I think wrongly, that 

 the proptosis must have been due to an excess of fat. The 

 circumstances of the case may equally well be accounted 

 for by a protrusion forward of orbital fat due to muscular 

 contraction. 



Though the vestigial character of the plica semilunaris 

 is well recognized, the vestigial character of the caruncle 

 seems to have been overlooked. A study of the morphol- 

 ogy of the parts about the inner canthus of the eye in mam- 

 mals shows variations of a marked character, not only in the 

 different natural orders, but also in the different species. 

 In kangaroos the inner canthus is prolonged into a triangular 

 flat area, kept moist by the overflow of tears; it is con- 

 tinuous with the skin of the nose and is fringed with fur. 

 A somewhat similar bald area, fringed with fur, is met with 

 in the Carnivora, .varying, however, in size and shape in 

 different species. It is among the Ungulata that the most 

 conspicuous developments are met with in this region, 

 more especially among the ruminants (Fig. 24). In them 

 the inner canthus is prolonged for a considerable distance 

 inward and downward, sometimes as a thin streak and 

 sometimes as a broad band. The band or streak ends 

 usually in an inverted fold, for the lodgment of which there 

 is, in some animals, a depression in the lacrimal bone. 

 This fold or recess is termed the "suborbital pit," and by 

 French naturalists, as it is kept moist by lacrimal secretion, 

 "larmier." The whole of the integumentary area leading 

 from the eye to the recess and the recess itself is composed 

 of numerous sebaceous glands opening into dwarfed hair- 

 follicles (Fig. 25); at the bottom of the recess a few short 

 hairs are frequently seen projecting from among the glands. 

 Around this glandular structure are bands of muscle fibers, 

 which by their contraction bring about a protrusion of the 



