83 



extensive musculature produces any considerable movement of the eyeball — it is 

 too firmly attached to the immovable optic cup — but the muscles probably 

 adjust the eye to the displacements produced by the flexures of the arms and head. 



The sclera is a hemispherical cup of cartilage whose margin is thick- 

 ened and slightl}- incurved. This cartilage consists of a single layer of flattened 

 cells lying bet^reen two sheets of matrix. Toward the rim uf the cup the cells 

 become cubical , then columnar and in the thickest part of the rim , they form 

 two or three layers of angular cells. The portions of the sclera that are not 

 covered or are only partially covered by the argentea of the iris are coated 

 externally by an argentea similar to that of the iris whose fibres , however , are 

 sinuous, longer and finer. 



The white bodies (see p. 65) are two irregular masses of problematical 

 tissue which are wedged in between the optic ganglion and the eye. The upper 

 white body lies upon the antero-dorsal surface of the eye while the lower fies 

 upon the postero-internal surface so that they are upon opposite sides of the 

 bundle of nerve fibres which passes between the eye and the optic ganglion. 

 A falciform bar of cartilage , attached by a fascia to the pedal process , lies 

 between the upper white body and the eye, and helps both to support the eye 

 and to protect the optic ganglion. The foramina in the sclera through which 

 the nerve fibres pass out from the retina are small , quite near together and 

 are situated in an elliptical area on the dorso-internal surface of the eye. The 

 longer axis of this area extends obliquely downward and forward. 



A sheet of connective tissue, the suspensory ligament of the lens, stretches 

 across the top of the sclerotic cup and supports both the ciliary body and 

 the lens. The peripheral portion of this ligament has attached to its inner sur- 

 face the fibres of a radial muscle , the ciliary muscle (of Langer) which arises 

 from the rim of the sclera. The intermediate zone of this ligament supports 

 the inner and outer portions of the ''ciliary body" or "corpus epitheliale" which 

 produce the inner and outer portions of the lens, respectively. The t^vo portions 

 of the ciliary body (Plate III , Fig. 20) arise from the inner and outer sheets of 

 ectoderm that form the outer w^all of the optic vescicle while the suspensory 

 ligament and cilary muscle arise from the mesoderm enclosed bet\veen the 

 ectodermal sheets. The cells of these sheets are at fii'st cubical but those at the 

 center of the innei- sheet soon produce small, finger-like processes, one for each 

 cell , which extend into the posterior chamber and , uniting , form a small club- 

 shaped body, the lens. The cells of the zone immediately around the center, 

 produce similar but longer processes which, extending toward the lens, unite 

 with one another and form one of the concentric laminae of the lens. The 



