280 



COMPARATIVE ANATOMY 



choroideal lymph-space, is a silvery or greenish-gold iridescent 

 membrane, the aryentca. It extends either over the whole interior 

 of the eye (Teleosts), or is limited to the iris (Elasmobranchs). A 

 second layer with a metallic lustre, the tapetum lucidum, is present 

 in Elasmobranchs internally to the iridescent portion, and within 

 this again is the layer of the choroid known as the choriocapillaris. 

 No tapetum appears to be present in Teleostei or Petromyzon. 



Fa, 



FIG. 206. LONGITUDINAL VERTICAL SECTION OF THE EYE OF DISSOMMA. 

 ( After A. Brauer. ) 



Ch, choroid ; Fa, fibres of the argentea ; LK, lens-cushion ; Lp, ligamentum 

 pectinatum ; M, smooth muscle ; o, optic nerve ; rr, accessory retina ; rr', 

 portion of accessory retina ; Sc, sclerotic. 



The so-called " choroid gland" present in many Teleostei and 

 in Amia, consists of a network of blood-vessels (rete mirabile) 

 which has the form of a cushion, lying near the entrance of the 

 optic nerve, between the argentea and pigment epithelium of the 

 retina; it thus has nothing to do with a "gland," and is in relation 

 to the pseudobrarich (cf. under Respiratory and Vascular organs). 



The eyes of certain deep-sea Teleosts are of particular interest, 



