. The development of the chick; an introduction to embryology . )tic cup. r., Retinal layer ofthe optic cup. of the iris is a narrow zone bounding the i)ti])il in which the twohirers of the oi)tic cup become blended so that jngnicnt fromthe outer layer invades the inner layer; the ci)itludia are decidedly ORGANS OF SPECIAL SENSE 273. Fig. 159. — P>ontal section of the eye of an eight day chick. ant. ch., Anterior chamber of the eye. ch., Choroid coat, cil., Ciharyprocesses. Corn., Cornea. 1. e. 1., Lower eyeHd. n. m., Nictitating mem-brane, Olfactory sac. op. n., Optic nerve, o. s., O
. The development of the chick; an introduction to embryology . )tic cup. r., Retinal layer ofthe optic cup. of the iris is a narrow zone bounding the i)ti])il in which the twohirers of the oi)tic cup become blended so that jngnicnt fromthe outer layer invades the inner layer; the ci)itludia are decidedly ORGANS OF SPECIAL SENSE 273. Fig. 159. — P>ontal section of the eye of an eight day chick. ant. ch., Anterior chamber of the eye. ch., Choroid coat, cil., Ciharyprocesses. Corn., Cornea. 1. e. 1., Lower eyeHd. n. m., Nictitating mem-brane, Olfactory sac. op. n., Optic nerve, o. s., Ora serrata. p.,Pigment hiyer of the optic cup. post, ch., Posterior chamber of the Retina, scl., Sclerotic coat. scl. C, Sclerotic cartilage, u. e. 1., L^ppereyelid. thinner than in the ciliary region. The mesenchyme oAcrlyingthe iris early becomes condensed to form the stroma of the iris;the epithelia form the uvea of the developed iris (Fig. L59).The muscles of the iris (sphincter pupilke) are stated by 274 THE DEVELOPMENT OF THE CHICK Nussbaniii, Szily. and Lewis to arise fiom ei)ithelial buds of thepupillary margin unci the adjacent portion of the pigment layerof the iris. The marginal buds (Fig. KK)) begin to form duringthe seventh day, the more i)eripheral ones somewhat later; theformer are less munerous and
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