88 EQUINE ANATOMY. 



Structure : a proper menbrane with unstriped muscular 

 fibres, an anterior epithelial layer, and a posterior 

 epithelial or uvea. 



5. Retina. — An expansion of the optic nerve. Struc- 

 ture : connective tissue forming the external and inter- 

 nal limitary membrane and nerve elements, forming 

 seven layers : 1 — one of rods and cones ; 2 — external 

 granular ; 3 — intermediate ; 4 — inner granular ; 5 — 

 molecular ; 6 — ganglionic ; 7 — of fibres of optic 

 nerves. 



Humours or media. — Crystalline lens, transparent 

 lens, enveloped by the crystalline capsula ; vitrous 

 humour covered by the hyaloid membrane; aquous 

 humour secreted by the membrane of Descemet or 

 Demours. 



Ear. — Division : External, middle and internal 

 ear. 



External. — Composed of: 1 — external auditory 

 canal, formed by the petrous portion of the temporal 

 bone; 2 — the concha or pavillion formed by the con- 

 chal, annular and scutiform cartilages, and moved by 

 ten muscles : 1 — Zygomatico auricularis. Synonyms. 

 Attolens anterior, (P). Temporo- auricularis, (L). At- 

 tachments : Zygomatic process of the temporal base of 

 the concha and external border of the scutiform carti- 

 lage. Action : Fulls the ear forward. 2 — Temporo- 



