150 Mammalia. Organ of Sight, 



2. Suspensory Muscle 



is divided 



in Cete into four short muscles, paralleling the longer recti, but 

 of greater breadth, and almost continuous. 



In Rhinoceros (Perissodactyla, Multungula) the fasciculi of the 

 Choanoid Muscle have coalesced into two masses. 



is alone present 



in the Balcence (Cete), in the absence of the other muscles of the 

 eye*. 



is rudimentary 



in lower Quadrumana; where a few fibres detached from the 

 inner part of the origin of the recti to be inserted into the sclerotic 

 nearer the entry of the Optic Nerve represent it. 



3. * Depressor' of lower eyelid. 



In Rhinoceros and Monotremata the lower eyelid has a depressor 

 muscle. 



4. ^ Nictitator'* muscle. 



In Elephas (Proboscidia) there is a special * nictitator' muscle, 

 the fibres of which pass at first over the base of the membrane in a 

 curve, then form an angle to include the extremity of the nictitating 

 cartilage, which is consequently moved in the diagonal of the con- 

 tracting forces. 



5. ' Orbicular^ muscle. 



In Cete, and Seals (Sectorialia) the circular palpebral opening is 

 closed by an * orbicular' muscle, or sphincter, and is expanded by 

 four broad, thin, almost continuous muscles {e.y. Porpoise). 



6. The Sclerotic coat. 



In the Ornithorhyncus the * Sclerotic' ib Jihro-cartilayinous. 

 In the Cete the Sclerotic is excessively thick, as also in the Pro- 

 boscidia, at the entrance of the optic nerve. 



7. The Pupil 



contracts to a vertical slit 



In the Pradypodidce (In-Enamellata) and the small crepuscular f 

 Felidae (Sectorialia). 



is transversely oblong 

 in Camel, Ox, and Sheep. 



* Mayer. t In the large diurnal Felidse it is circular. 



