1 3 o 



ANIMAL BIOLOGY. 



[Part I. 



crystalline lens is attached to the sides of the eyeball by the 

 suspensory ligament. It is contained in a delicate capsule. By 

 the action of special muscles (ciliary) the convexity of the 

 anterior face of the lens can be altered, so as to allow of the 

 focussing of the image on the retina. 



Cut the remainder of the capsule in half by an incision at 

 right angles to the axis of the eye. Note the optic nerve, 



FIG. 42. DIAGRAMS OF EVE DEVELOPMENT. 



A. Transverse section, showing the diverticulum of the brain (o.v.) meeting 

 the invagination of the surface (o.p.). B. Transverse section at a later stage, 

 showing the lens derived from the surface invagination lying in the pushed- 

 in diverticulum of the brain. C. The optic cup derived from the diverticu- 

 lum of the brain seen from the ventral aspect. D. Section of the eye. 



Isf v. First vesicle of the brain (fore-brain), aq. h. Aqueous humour. 

 ch. Choroid. ch. f. Choroid fissure, cor. Cornea, cor. ep. Corneal epithe- 

 lium, ir. Iris. I. Lens. I. r. Limits of the retina proper, o. c. Optic cup. 

 o. p. Optic pit. o. v. Optic vesicle, op. n. Optic nerve, pu. Pupil, scl. 

 Sclerotic, v. h. Vitreous humour. 



which will be seen to enter the back of the capsule ; also 

 jelly-like substance (vitreous humour, v. h.) with which this 

 posterior chamber of the eye is filled. Lining the interior of 



