346 NORMAL HISTOLOGY. 



The ciliary muscle presents a conspicuous thickening for about 

 i mm. , which extends from the orbicular zone to the base of the iris 

 and bears on its inner surface the connective-tissue stroma of the 

 ciliary processes and the orbicular ring. In meridional sections its 

 mass appears as a triangular area, the cross-section of a three-sided 

 annular band of muscle entirely encircling the eyeball. The 

 triangle thus formed closely approximates a right angle whose sides 

 are unequal ; the shorter anterior side extends from the sclero- 

 corneal juncture towards the ciliary processes, and the longer inner 

 border is prolonged to meet the outer side or hypothenuse at an 

 acute angle at the anterior border of the choroid. 



The mass of the ciliary muscle consists of interlacing bundles 

 of involuntary muscle, the interspaces between which are filled 

 by connective tissue. The muscular fasciculi are arranged as 

 three sets, the meridional, the radial, and the circular. The 

 meridional fibres lie generally parallel to the sclera, and form a 

 compact layer attached in front at the sclero-corneal junction, 

 near the anterior margin of Schlemm's canal, and behind at the 

 fore margin of the choroid, where, in common with many of the 

 radial fibres, it finds insertion ; in recognition of this attachment, the 

 meridional and radial fibres were named the tensor choroidese. 

 The radial bundles spread out fan-like from their anterior attach- 

 ment, the most external fibres running nearly parallel to the meridio- 

 nal bundles, with which they become continuous, while the anterior 

 pass off at a considerable angle. The circular fibres, the ring-mus- 

 cle of Miiller, constitute a distinct group of equatorially-disposed 

 bundles, which occupy the internal angle of the ciliary muscle and 

 extend at right angles to the preceding bundles. 



The blood-vessels of the ciliary body are especially concerned 

 in supplying the ciliary muscle, to which minute arterial twigs 

 pass from the imperfect vascular circle lying behind the arterial 

 circle of the iris. 



The numerous nerves of the ciliary muscle are derivatives of the 

 ciliary trunks, which on entering the muscle form a plexus within 

 its substance ; from this plexus fibres pass internally to the iris, 

 outwardly to the cornea, while others are distributed to the 

 ciliary muscle itself. Small ganglion-cells also occur, singly or 

 in small groups. 



THE IRIS. 



The iris constitutes the anterior segment of the uveal tract, and 

 consists of a principal stroma-layer covered in front by a reflection 

 of the corneal endothelium and behind by the continuation of the 

 deeply-pigmented rudimentary retinal layers the pars iridica 



