CILIARY MUSCLE AND LIGAMENT. 721 



The vessels and nerves have a radiating arrangement through the stroma; the former 

 giving rise to rings, one at the circumference, the other near the pupil ; and the latter 

 forming a network. (See the description of the vessels and nerves of the vascular 

 coat.) 



Pupillary membrane (membrana pupillaris). In foetal life a delicate transparent 

 membrane thus named closes the pupil, and completes the curtain of the iris. The 

 pupillary membrane contains minute vessels, continuous with those of the iris and of 

 the capsule of the crystalline lens; they are arranged in loops, which converge towards 

 each other, but do not quite meet at the centre of the pupil. At about the seventh or 

 eighth month of foatal life these vessels gradually disappear; and, in proportion as the 

 vascularity diminishes, the membrane itself is absorbed from near the centre towards 

 the circumference. At the period of birth, often a few shreds, sometimes a larger 

 portion, and occasionally the whole membrane is found persistent. (See also the 

 account of the development of the eye.) 



CILIARY MUSCLE, LIG AMENTUM PECTINATUM, AND CIRCULAR SINUS. 



When the outer coat of the eyeball is separated from the choroid, a circular 

 groove is seen passing round on the inner surface of the sclerotic, at its 

 corneal margin. This groove is the outer wall of a venous canal, the sinus 

 circularis iridis or canal of Schlemm. On the middle coat a corresponding 

 groove, which completes the canal, is seen, and this is bounded in front 

 by a torn membranous edge bounding the anterior surface of the iris, the 

 ligameutum pectinatum, while the thickest part of the white ring of the 

 ciliary muscle is behind it. This canal communicates with other venous 

 spaces which give an erectile appearance to the tissue at the base of the 

 ciliary processes. 



The ligamentum pectinatum consists of slight festoon-like processes of the 

 fibres of the iris, lying in a transparent elastic fibrous tissue continuous with 

 the posterior elastic layer of the cornea. It is a more developed structure 

 in the eyes of the sheep and ox than in the human eye, and in them the 

 festooned processes are prominent, giving a milled appearance like that of the 

 edge of a coin. 



The ciliary muscle (Bowman) forms a ring of unstriped muscular tissue 

 about T ^th of an inch broad on the fore part of the choroid. Its fibres, 

 yellowish-white in colour, and longitudinal in direction, are attached in front 

 to the inner surface of the sclerotic coat ; and are also connected with the 

 terminal fibres of the posterior elastic layer of the cornea. From that 

 origin the fibres are directed inwards and backwards in a manner which in 

 a section appears radiated, and end by joining the choroid coat opposite and 

 beyond the ciliary processes. The muscle is soft, and ramified pigment-cells 

 are scattered through its substance. 



Concealed by the longitudinal or radiated fibres is a ring of fibres taking 

 a circular direction, and which were still described as the ciliary ligament 

 after the radiated fibres had been admitted to be muscular. This set consti- 

 tutes the circular muscle of H. Miiller. 



The ciliary muscle appears to be in some way effective in producing the 

 change in the form of the lens which takes place in accommodation of the 

 eye to near vision (see Allen Thomson in " Glasgow Medical Journal" for 

 1857). 



VESSELS AND NERVES OF THE MIDDLE TUNIC OF THE EYE. 



The arteries of the choroid and the ciliary processes are derived from the 

 posterior and anterior ciliary vessels. The posterior consist of two sets, distin- 

 guished as the short and the long. The short (posterior) ciliary branches of the 



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