Human anatomy, including structure and development and practical considerations . ed as to be indistinguishable without bleaching the tissue. The dilatatormuscle is developed from the outer layer of fusiform cells, so that it represents anepithelial Cectoblastic) muscle. The inner cells are larger polygonal elements, whichgradually lose their pigment as they approach the ciliary processes. Over the latterthey contain no pigment, whereas the outer cells remain pigmented. The blood-vessels of the iris pass radially inward from the circulus arteriosus iridismajor at the periphery. Near the pupill
Human anatomy, including structure and development and practical considerations . ed as to be indistinguishable without bleaching the tissue. The dilatatormuscle is developed from the outer layer of fusiform cells, so that it represents anepithelial Cectoblastic) muscle. The inner cells are larger polygonal elements, whichgradually lose their pigment as they approach the ciliary processes. Over the latterthey contain no pigment, whereas the outer cells remain pigmented. The blood-vessels of the iris pass radially inward from the circulus arteriosus iridismajor at the periphery. Near the pupillary border, they form a second ring, the cir-cnlus arteriosus iridis yninor, branches from which supply the sphincter muscle and thepupillary zone. The venons radicles unite to form trunks which accompany thosefrom the ciliary processes to empty into the vencs vorticosce. The lymphatics are represented by the interfascicular clefts which communicatewith the anterior chamber, with the spaces within the ciliary body, and with thespaces of Fontana, Veins drainingciliary processes. Choroidal veins- Injected ciliary processes and iris;posterior surface. from the PRACTICAL CONSIDERATIONS : THE IRIS. 1461 The nerves of the iris are branches of the ciHary nerves. They follow the courseof the blood-vessels and, branching, form a plexus of communicating nonmedullatedfibres, which supply sensory, motor and vasomotor impulses. The human iris prob-ably contains no ganglion cells. Practical Considerations.—The iris may be partially or completely absent,when l)v l)ringing down the eyebrows and i)artially closing the lids, the patientwill make an effort to shut off the excess of light, as in albinism, and the eye willfrequeiuly be nystagmic. A coiirenital cohboma or deficiency in the iris is usually in the lower part, andmay be associated with a corresponding defect in the ciliary body and choroid. Thepupil may be eccentric in position (corectopia), unusually small (microcoriaJ,irregular in
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