344 NORMAL HISTOLOGY. 



side, at right angles to the outer, extends inwards from the pectinate ligament 

 towards the lens/ The ciliary body presents three subdivisions: the ciliary 

 ring, the ciliary processes, and the ciliary muscle. 



The ciliary ring, or orbiculus ciliaris, consists of a smooth band of 

 tissue, 4 mm. in width, in advance of the ora serrata. It differs in structure 

 from the choroid in the absence of the choriocapillaris, its vessels running in 

 a longitudinal direction and returning the blood from the iris and ciliary 



Cornea Canal of Schlemm 



. Pectinate ligament 



Ciliary muscle (radial fibres) 

 lera 



eridional fibres 



Ciliary processes Circular fibres Choroid Pars ciliaris retinae 



FIG. 392. Meridional section of ciliary region, showing ciliary body with its muscle and processes. X 40. 



body to the venae vorticosae. On its inner surface, delicate meridionally 

 placed folds make their appearance, by the union of which the ciliary 

 processes are formed. 



The ciliary processes constitute the remaining portion (2.5 mm.) 

 of the ciliary body. They form an annular series of folds, about seventy in 

 number, which surround the lens and act as points of attachment to its sus- 

 pensory ligament. Commencing by the union of several plications of the 

 orbiculus ciliaris, they rapidly increase in height and breadth, until they reach 

 an elevation of from .6-. 8 mm., and then fall suddenly to the iris-level. 

 They consist of a rich network of vessels embedded in a pigmented con- 

 nective tissue stroma, like that of the choroid. The inner surface is covered 

 with a homogeneous membrane, continuous with the membrana vitrea of the 

 choroid, on the inner surface of which is placed the double layer of cells 

 representing the ciliary portion of the retina {pars ciliaris retina). Each 

 ciliary process is composed of a number of irregularly projecting folds which 

 increase in height as the iris is approached. 



The ciliary muscle occupies the outer portion of the ciliary body, 

 lying between the sclera and the ciliary processes. It forms an annular pris- 

 matic band of involuntary muscle, which in meridional sections has a trian- 

 gular form. Its main fibres arise from the sclera and pectinate ligament, at 

 the sclero-corneal junction internal to the canal of Schlemm, and run in a 

 meridional direction backwards along the sclera to be inserted into the cho- 

 roidal stroma. The inner angle of the triangle, at the base of the iris, is 

 occupied by a band of circularly disposed fibres, the circular ciliary muscle 

 of Miiller. Between the circular and meridional portions, the fibres assume 

 a radial direction and are separated by considerable connective tissue, which 

 in the deeply pigmented races may contain many branched pigmented cells, 

 but in the white races is free from pigment. Acting from its origin, the cil- 

 iary muscle draws forward the ciliary processes and relaxes the lens-capsule. 



