DORSO-VENTRAL SECTION OF THE EYE. 525 



Glandula Harden (Gl. Harder). A small lachrymal gland pouring out a lubricator 

 on the ental or concave surface of the Mb. nictitans ( 1403, B). 



Iris. This is the contractile diaphragm just cephalad of the lens. Its cut edges are 

 shown in the figure, and it is represented as dilated to a circle ( 1418). Its muscles are 

 of the unstriped variety, yet they act rapidly and appear as if almost voluntary in the cat. 



Lens. The lens in the cat is double convex as in man, but unlike the human lens, 

 that of the cat is the more convex cephalad ( 1428). 



Discus opticus (Mel.)- The white or blind spot of the eye. It is the end of the 

 optic nerve as it enters the eyeball. 



Membrana (Mb.) nictitans. This is the internal or third eyelid. It has a black free 

 border ( 1402). 



Mucosa. Mucous membrane of the roof of the mouth. 



M. ciliaris (M. c.). The ciliary muscle. This is attached to the sclerotica and cho- 

 roidea. By its contraction and relaxation the lens is made more or less convex, and hence 

 accommodates the eye for near or distant objects. The limits of this muscle have not 

 been satisfactorily determined m the cat. 



M. levator palpebrae dorsalis (M. Iv. plpbr.). The elevator of the dorsal (superior, 

 upper) lid is a slender muscle. It must be greatly aided by the ectal muscles of the head. 



M. rectus dorsalis (superior), (M. r. drsl.). The dorsal straight muscle of the eye. 

 It is cut longitudinally, hence its tendon, is seen on edge. 



M. rectus lateralis (externus), (M. r. Itrl.). The muscle is cut and reflected ventrad 

 to show its origin from the bony septum between the Fm. op. and Fm. 1. a., and also that 

 it is between the tendon of the ventral rectus and the common tendon of the choanoid 

 muscles ( 1405). 



M. rectus ventralis (inferior), (M. r. vntr.). The ventral rectus has been divided 

 longitudinally and is seen on edge. Its origin is from the lateral wall of the Fm. 1. a. 



M. choanoideus mesalis (M. ch. m.). The tendon of this muscle crosses the optic 

 nerve as shown. 



M. choanoideus dorsalis (M. ch. drsl.). This muscle and its tendon are seen on edge, 



M. choanoideus lateralis (M. ch. 1.). The tendon of this muscle is seen in its width. 



M. choanoideus ventralis (M. ch. vntr.). The ventral of the choanoid muscles. 

 The common tendon of the choanoids seems to be a continuation of this as it goes to its 

 origin from the Fm. 1. a. ( 1413). 



M. obliquus ventralis (inferior), (M. oblq. vntr.). The cut end of the ventral oblique 

 muscle ( 1406). 



M. orbicularis palpebrarum (M. orb. plpbr.). The cut ends of this circular muscle 

 are shown in each lid. The ectal muscles of the head mingle with this, but they are 

 omitted from, the figure. 



M. pterygoideus. This corresponds to the external pterygoid of man. It passes from 

 the O. palatinum to the mesal side of the mandible (Straus-Durckheim, A, II, 217). 



N. maxillaris superior (N. mx. spr.). The second division of the trigeminus nerve. 

 Its distribution is given in the Table ( 1392). 



N. opticus (N. op.). The optic nerve is seen traversing the optic foramen on its way 

 to the eyeball. It is surrounded by dura which is continuous with the sclerotica. 



Ora serrata (Ora sr.). The retina at the beginning of the ciliary plicae becomes thin, 

 and, as in man it is somewhat indented, it is called ora serrata. The serrated appearance 

 is not marked in the cat. The retina is very thin from the ora to the tips of the ciliary 

 processes, where it ceases. This part of the retina is called the pars ciliaris retina3 ( 1424), 



O. frontis. The frontal bone ( 516). 



O. orbito-sphenoideum (O orsph.), ( 515). 



