262 EFFA FUNK MUHSE. 



sac is thus formed and the layers over the eye between this sac 

 and the exterior form the "brille." 



Six weakly developed muscles are present. The four straight 

 ones arise in the neighborhood of the foramen opticus, while the 

 two oblique ones arise from the surface of the prefrontal which 

 is turned toward the eye socket. 



Closely connected with the eye is a gland, Harder's, whose 

 function is doubtful. Leading from this gland is a single duct, 

 which either empties into the duct from Jacobson's gland or di- 

 rectly into the mouth cavity. The secretions of the gland are 

 thus not functional in connection with the eye. 



The sclera consists of closely woven fibers. Ciliary muscles 

 are not found, but next to the iris is a great bundle of equatorial 

 muscle fibers running obliquely, which seem to be a continua- 

 tion of the iris musculature. The ciliary processes are weakly 

 developed. 



The retina consists of the usual layers. The nerve fiber layer 

 is very thin (.003-. 004 mm.). 



The ganglion cell layer consists of a single, rarely two layers 

 of small cells, each with a very large nucleus (.OI2-.OI3 mm.). 

 The inner reticular layer contains, at apparently regular inter- 

 vals, elongated, oval nuclei (.042 .045 mm.). 



The inner nuclear layer consists of two kinds of cells (.052- 

 .054 mm.). 



The outer reticular layer is very thin (.004 .005 mm.). 

 The sensory epithelium consists of the outer nuclear layer and 

 the cone layer which is made up of single and twin cones. There 

 are no rods. A single cone consists of two sections, an outer 

 extremely small section, 56 microns in length and an inner 

 much larger section, almost completely filled with a larger, pear- 

 shaped, strongly refractive body, the ellipsoid, 14-16 microns 

 in length and 8-9 microns across its widest part, which is turned 

 toward the limiting membrane. The twin cone consists of two 

 parts, one similar to a simple cone, the other cylindrical and very 

 slender, its structure being otherwise like that of a simple cone. 

 It is probable that the two parts of the twin cone are connected 

 with but one nucleus. The nuclei of the cones vary greatly in 

 form and leading from these into the inner layers of the retina 

 are relatively very large fibers or processes. 



