46 



PLATE XXII. 



THE FROGr — continued. 



Sense Organs — 



Fig. 1. Eve of Ox divided — (a) Into a right and left lialf — left half shown. 



{b, c) Along equator into an anterior and posterior half. 

 Sclerotic or outer coat passing into tiaasparent cornea in front. 



Choroid coat pigmented, anterior end raised into longitudinal plaits — the ciliary processes. 

 Iris (L. a rainbow), anterior to ciliary processes, and connected to sclerotic where it passes into 



cornea by the ciliary muscle. 

 Lens enclosed in capsule, which is attached to the inner side of the choroid by suspensory 

 ligament. 

 CSliary muscle dips into folds of uiliary processes above, just as suspensory ligament dips into them below (i). 

 Aqueous humom- anterior to lens. 

 Yitreous humour posterior to lens. 

 Retina inside choroid. 



Optic nerve entering a little to one side of axis by the optic pore. 

 Fig. 1 c. Blood-vessels are seen to enter retina from the spot where optic nerve enters. 

 Fig. 2. Oeneral View of Eight Ear of Frog — 



Tympanic cavity exposed by removing tympanic membrane. 

 Three semicircular canals. 

 Columella auris (L. little column of the ear). 

 Fig. 3. ]\[embranous L.^byrinth of Left Ear — 



Semicircular canals, anterior, posterior, and horizontal, each dilated at one end into ampullae 

 (L. ampullor, I swell out), and two ends of vertical canals joining together. 

 f Utriculus (L. a little bag), into which semicircular canals open. 

 Vestibule | <^^^^^^^ ^l a small bag). 



Cochlea (L. a snail's shell), rudimentary. 



Fig. 4. Essential Parts of Human Ear, natural size — 



External ear — Pinna or concha (L. a shell), not shown. 



Auditory meatus (L. a canal). 



Tympanic membrane. 



Tympanic cavity or tympanum opening by Eustachian tube into pharynx. 



{ Malleus (L. a hammer). 



Middle ear / Auditory ossicles or ear-bones bridging over cavity -< Incus (L. an anvil). 



(^ Stapes (L. a stirrup). 



Fenes'tra ovalis (L. oval window), an oval membrane, to which foot-plate of 



stapes is attached. 



Fenestra rotunda (L. round window), at the base of cochlea. 



( Semicircular canals, horizontal not shown. 

 Internal ear or i „,.,,. , , . , , 



. , . , -; Vestibule into wluch canals open. 



( Cochlea, also communicating with vestibule. 



Fig. .'). Auditory Ossicles of Human E.\r, magnified. 



Fig. 6. Columella Auris detached (see also fig. 2) — • 



Stapes or inner end fits into fenestra ovalis. 



Extra-stapedial or outer end attached to tympanic membrane. 



