ACCOMMODATION AND CONVERGENCE 69 



stretched, the ciliary processes are drawn backward, and 

 the spaces in the tissue immediately external to them are 

 also drawn backward and elongated out. The fibers of the 

 ciliary muscle contained in these spaces become likewise 

 altered in their direction, and assume a longitudinal position 

 antero-posteriorly instead of running circularly. 



In hypermetropia, where the eyeball is abnormally short 

 from before backward and not fully developed, the ciliary 

 processes, as in the embryonic condition and as in the 

 low r er animals, project farther forward and inward, so that 

 the spaces external to them, and the muscle fibers contained 

 therein, have a circular direction. 



In animals below Primates in which the ciliary muscle 

 has scarcely any more fixed point of attachment anteriorly 

 than it has posteriorly, and where its fibers have all a longi- 

 tudinal direction, the effect of their contraction w r ould appear 

 to produce a drawing together, or rucking up, of the inner 

 surface of the ciliary body, much in the same way as con- 

 traction of the dilator muscle fibers of the iris draws together 

 or rucks up the iris in dilation of the pupil (Fig. 14). In 

 apes and in man the concentration together of the fibers of 

 the pectinate ligament at the sclero-corneal margin pro^ 

 duces a sort of tendon, or fixed point of origin, to the ciliary 

 muscle. So that on its contraction the tissue into which 

 it is inserted is drawn forward toward this fixed point. 



A study of the morphology and embryology of the lens 

 and its suspensory ligament seems to leave no doubt that 

 the effect of contraction of the ciliary muscle is, as Helm- 

 holtz pointed out, a slacking of the suspensory ligament 

 and a relaxation of tension in the lens fibers. 



The following table gives the measurements of the antero- 

 posterior and lateral diameters of the lens in the eyes of 

 several different mammals: 



