CHAP, in.] SIGHT. 977 



A portion of the tendon of the levator palpebrae closely 

 united with an extension of the tendon of the superior rectus is 

 inserted into the hinder part of the upper eyelid, where the con- 

 junctiva lining it is about to be reflected over the eyeball , and 

 a similar extension of the inferior rectus is similarly inserted 

 into the lower eyelid. Hence a contraction of the superior 

 rectus, while elevating the visual axis, at the same time raises 

 somewhat the upper eyelid ; and in like manner the inferior rec- 

 tus, while depressing the visual axis, lowers the lower eyelid. 



Between the main tendon of the levator palpebrae and the 

 tendinous slip just mentioned lies a small bundle of plain, un- 

 striated muscular fibres, which starting from the levator, ends 

 in the hind border of the tarsus ; it is sometimes spoken of as 

 the middle insertion of the levator. A similar bundle of plain 

 muscular fibres connects the insertion of the inferior rectus with 

 the tarsus of the lower eyelid. These two small plain unstriated 

 muscles appear to be governed by nervous filaments proceeding 

 from the cervical sympathetic, stimulation of the cervical sym- 

 pathetic leading to contraction of these muscles and so to a 

 partial opening of the eye, and section of the same nerve pre- 

 venting their being thrown into contraction and so contributing 

 to closure of the eyelids. In some of the lower animals this 

 closure of the eye upon section and opening upon stimulation 

 of the cervical sympathetic is very distinct. In those animals 

 which possess a third eyelid this is retracted by stimulation and 

 comes forward upon section of the cervical sympathetic. 



Stimulation of the cervical sympathetic also causes some 

 protrusion and section causes recession of the whole eyeball ; 

 this is seen at times in ma*i in disease. 



609. The conjunctiva which lines the ocular surface of 

 the eyelids and is reflected from them over the eyeball, the line 

 along which reflection takes place being spoken of as the /<>////> 

 conjunctive consists like the skin of the body of which it is a 

 continuation, of an epithelium or epidermis resting on a dermis 

 of connective tissue. It differs from the skin in the dermis 

 being delicate and in the epidermis being thin with a tendency 

 for the constituent cells to become columnar; hence it is some- 

 times spoken of as a " mucous membrane." On the ocular 

 surface of the eyelids the conjunctiva is thrown into irregular 

 ridges or imperfect and fused papillae, giving rise to a satiny 

 appearance ; here the epithelium consists of several layers of 

 cells, the uppermost of which are fattened* Over the fornix, 

 the epithelium consists of two or three layers only, the cells 

 in the uppermost layer being cubical or columnar ; over the bulb 

 the epithelium consists also of a few layers only, the upper cells 

 being somewhat flattened and the dermis being thrown up into 

 scattered papillae. 



Imbedded in the tarsus, stretching from the hind border t<t 



62 



