274 ORGANS OF THE SENSES. 



is fully developed, is here as in the quadrumana reduced to 

 the small follicles of the caruncula lachrymalis, as the great 

 membrana nictitans is now merely a small plica semilunaris 

 at the inner angle of the eye. The lympid fluid from the 

 bilobate lachrymal gland, conveyed by the upper eye-lid 

 over the conjunctiva, passes through the two puncta lachry- 

 malia near the inner angle of the eye, and through the two 

 small lachrymal ducts to their dilated sac and tapering canal 

 from which it is poured by a valvular orifice into the anterior 

 part of the inferior meatus of the nose. The eye-balls, 

 nearly spherical in form, with their axes parallel, and 

 perforated behind by the optic nerves on the nasal side 

 of their axes, are supported on the l>ack part by a large 

 deposit of adipose substance (105. /. /.) and are moved 

 by four recti and two oblique muscles; the tendon of 

 the superior oblique is not perforated by the rectus su- 

 perior (105. o.) as it is in many feline animals. The 

 muscles are inserted into the white anterior part of the 

 sclerotic, called tunica albuginea, and the optic nerve per- 

 forates a circular cribriform portion of this membrane behind, 

 the central minute aperture of which is occupied by the 

 central artery of the retina which passes through the middle 

 of the optic nerve (105. a.) The transparent cornea, com- 

 posed of homogeneous concentric laminae, thicker and more 

 convex than the sclerotic, has still its transverse diameter 

 a little more extended than its vertical. The choroid is 

 firmly united to the sclerotic at the white ciliary ligament 

 a line in breadth, and is perforated by a circular aperture 

 behind for the transmission of the optic nerve, and from 

 the anterior margin of this ligament proceed the numerous 

 minute folds of the corpus ciliare which give attachment 

 to about seventy ciliary processes (105, /.) extending with 

 their convex margins internally to be united to the capsule 

 of the crystalline lens. The villous internal surface of the 

 vascular layer of the choroid secretes, a layer of variable 

 thickness, of a muscous and viscid pigmentum nigrum 

 this appears to be immediately lined with the delicate 

 transparent membrane of Jacob, within which are the me- 

 dullary and fibrous layers of the retina (105. d.) and the 

 several concentric layers of the hyaloid membrane of the vi- 

 treous humour. The iris, composed chiefly of radiating vessels 



