SENSITIVE SYSTEM. 393 



membrane is double : one part of it lines the hollow containing 

 the lens ; the other advances under the ciliary processes, for 

 whose reception it is arranged into an equal number of radiated 

 longitudinal folds, with depressions between them, which proceed 

 to the border of the lens and adhere to the anterior circum- 

 ference of its capsule. The portion of black pigment between 

 the ciliary processes and these plicae adheres to both : so that 

 when the processes are stripped off, the plicae are seen marked 

 with a regular series of black striae forming a radiated circle 

 around the lens, which appearance has obtained the name for 

 this folded portion of membrane of memhramda corona ciliaris. 

 This being the arrangement of the divisions of the hyaloid mem- 

 brane, it follows that there must necessarily exist a triangular 

 interval or canal around the capsule of the lens, which forms the 

 base of it, having indentations in its front side: this is the canal 

 of Petit — canalis Pelitianus. This canal possesses the breadth 

 of the corpus ciliare, behind which it is readily inflatible. It 

 has no communication with any other part. 



The Ji aid that escapes from the punctured vitreous mass, 

 though of greater specific gravity, is much the same in appear- 

 ance as the aqueous humour, from which, I believe, it only differs 

 in the proportion, not in the number or nature, of its ingre- 

 dients— ?;/z. albumen, gelatine, common salt, and water. 



The arteiia centralis retina takes its course through the middle 

 of the vitreous humour to the capsule of the lens : but for all 

 this, anatomists have not succeeded in detecting any signs of 

 vascularity or organization in this extremely delicate tremulous 

 mass. 



OF THE EAR. 

 The organ of hearing is constituted of divers parts, 

 which have been arranged in two classes — the external and 

 the internal ear. 



The External Ear, 

 Comprises the Concha and the Meatus Auditor ius Ext emus. 



Concha*. 



The concha, or conch, is the term we use to denote the 

 whole of that part of the organ which is exposed to external view. 

 This consists of a flexible, trumpet-shaped, moveable structure, 



* In g'eneral form and external appearance the horse's ear bears no sort 

 of comparison with the ear of a man. The external ear of the latter, alto- 

 gether, has got the appellation of pinna; and on examining the surface of 

 a well-formed human ear, we perceive five eminences, the heiia;, antihelix, 

 3 E 



