574 THE EYE-LIDS. [sect. 229. 



the substance of the vitreous body separates from the fibrous 

 lamina, a limitary membrane, even more delicate than formerly, 

 makes its appearance, and forming the posterior Avail of Petit's 

 canal, extends up to the border of the lens; from this point it is 

 no longer traceable as a special membrane, the vitreous body 

 becoming most intimately united with the posterior lamina of the 

 capsule of the lens. 



Of the authors who have recently investigated the vitreous body, Fink- 

 beiner, employing corrosive sublimate, obtains results somewhat similar to 

 those of Hannover ; but, in several respects, his account does not appear 

 satisfactory. — Doncan, on the other hand, adopts views which are nearly iden- 

 tical with those of Virchow and myself. He lays special stress on the fact 

 that a fluid escapes from the cut surface of the vitreous body, leaving a com- 

 pacter substance behind. He finds no trace of the membranes described by 

 Hannover, either in the fresh corpus vitreum, nor after treatment with acetate 

 of lead and chromic acid. This author is uncertain whether the striated, 

 radiating appearance observed in chromic acid preparations indicates a sepa- 

 ration of the vitreous body into definite zones, or whether it is only an arti- 

 ficial effect. Doncan regards the peculiar motion of muscte volitantes as being 

 opposed to Hannover's theory of the structure of the vitreous body. Although 

 not in a position to demonstrate his views conclusively, Doncan is inclined to 

 regard this body as being made up of definite spaces containing a fluid ; and 

 he concludes, from the motion of muscse volitantes, and from other consider- 

 ations, that these spaces are disposed vertically in the hinder part of the 

 organ, and transversely in the anterior portion. 



In the neighbourhood of the entrance of the optic nerve, 71. Mailer has 

 found, on the hyaloid membrane, a somewhat knotted network with a few 

 nuclei, probably the remains of the foetal vessels. A similar structure is 

 found in the eyes of animals, on the obliterated hyaloid artery. 



B. ACCESSORY ORGANS. 



§ 229. The Eye-lids receive their shape from two structures, 

 named the cartilages of the eye-lids, or tarsi, which are thin, semi- 

 lunar plates, pliant but very elastic, and fastened together, both 

 internally and externally, by fibrous ligaments (the lig. tarsi). 

 The histological relation of these plates is with firm connective 

 tissue, although they occasionally contain a certain number of 

 small cartilage cells ; they measure 0-3'" to 0-4'" in thickness, and 

 their fibres run chiefly parallel to their borders ; they are covered 

 externally by the orbicularis palpebrarum and the skin, and in- 

 ternally by the conjunctiva. The external skin is here very thin 

 (£"' to 1'"), and the subcutaneous connective tissue is thin, loose, 

 and free from fat ; its epidermis is delicate (crc^'" to 0-058'" in 

 thickness), and it is provided with short papilla? (- B \"' to -^") ; it 



