410 JAMES ROLLIN SLONAKER 



The ciliary processes extend to the lens and are closely apphed 

 to its surface for about .7 mm. from the equator forward. The 

 attachment of these processes to the lens is so firm that when the 

 lens is separated from them and removed, portions of the pig- 

 ment remain attached to it. Since the ciliary bodies are directly 

 attached to the lens, a suspensory ligament is not necessary in 

 the sparrow eye. . . 



Still farther forward the chorioid is developed into the iris. 

 The pars ciliaris retinae, now composed wholly of the pigmented 

 portion or uvea, is contiaued forward to the edge of the pupil 

 and forms the pars retinalis iridis, the posterior layer of the iris 

 (plate 10, fig. 62, uv). At its circumference the iris is directly 

 connected to the chorioid and ciliary processes, and by the liga- 

 mentum pectinatum to the cornea (fig. 28). According to 

 Kolliker ('89), Schwalbe (70) and Pflugk ('06) the fibers com- 

 posing the ligamentum pectinatum are elastic. The endothelial 

 cells of the membrane of Descemet extend from the corneal 

 margin over the front of the iris. 



The inner portion of the iris is composed of a delicate frame- 

 work of connective tissue, numerous blood-vessels and nerves 

 and muscle fibers. Pigment cells are scattered in the anterior 

 portion. These are similar to those of the chorioid and have 

 the same origin. The various colors of the iris found in different 

 species of birds is due to this pigment. In the sparrow these 

 pigment cells are brown and give the chocolate-brown color to 

 the eye of the living bird. 



The muscles of the iris consist of striated muscle fibers ar- 

 ranged in two layers. The anterior layer is much thicker than 

 the posterior. It consists of circular fibers which form the 

 sphincter muscle of the iris. These fibers are most abundant 

 toward the circumference of the iris. Toward the margin of the 

 pupil they are reduced to about one-fourth the maximum thick- 

 ness. Toward the periphery these circular fibers become grad- 

 ually less and less numerous, more widely separated, and wholly 

 disappear at the base of the iiis (plate 10, fig. 62, cm, and fig. 

 28, C). The posterior layer of muscle tissue, composed of 

 radially arranged fibers one or two cells thick, is very thin. 



