516 AyATOJnCAL tecu^-ology. 



be seen easily by drawing the eyelids well apart and looking with, a 

 magnifier at their free edges near the mesal canthus. Insert a 

 beaded bristle into each canal. 



Lachrymal Duct. — This is formed by the union of the two canals 

 and extends to the nasal cavity. Its beginning is somewhat dilated 

 and is called the lachrymal sac. 



Demonstration.— SiigMlj expand the prsenaris and push the 

 beaded bristles mentioned above until they appear at the nasal 

 opening of the lachrymal duct. This opening is just ventrad of the 

 cartilaginous prolongation of the maxillo-turbinal bone (at a point 

 ventrad of the M of the abbreviation " Mxtrb." in Fig. 88). The 

 opening is quite large and will readily receive the probe of the tracer. 

 If it is desirable to trace the lachrymal duct throughout its course, 

 a bristle should be put into it. Then the head should be hemi- 

 sected, and the duct traced with nippers and arthrotome, com- 

 mencing at its nasal termination. 



MUSCLES OF THE EYE. 



The cat's eye possesses 12 muscles, ten belonging to the eyeball 

 (4 recti, 4 choanoid, the trocMearis and the ohliquus ventralis\ and 

 2 to the lids— o7'Mcularis palpebrarum (§ 1404) and levator palpe- 

 hrcB dorsalis (§ 1409). Besides the special muscles of the eyelids, 

 the muscles of the face assist and modify their movements. 



§ 1404. M. orbicularis palpebrarum (Fig. 126, M. orb. plpbr). 

 — This is the circular muscle surrounding both lids and serving to 

 close them. To demonstrate it, cut either of the lids transversely. 

 Just entad of the skin will be seen the cut ends of a thin layer of 

 pale, striated muscular fibers. The fibers are plentifully mixed 

 with elastic and white connective tissue. 



For the M. levator palpebrse dorsalis, see § 1409. 



§ 1405. Exposure of the Muscles of the Eyeball. — These as 

 well as the levator palpehra are within the orbital fossa. To expose 

 them, cut with nippers the two ends of the zygoma (Fig. 56). Grasp 

 the orbital process with the forceps and lateriduct it. At the same 

 time sever the soft parts close to the bone with an arthrotome, so 

 that the zygoma can be removed. Remove the temporal and mas- 

 seter muscles by grasping their cephalic edge and severing the 

 attachments. In doing this, be very careful not to include any of 

 the fibrous capsule of the eye. After these muscles are removed, 

 nip away half of the mandible ; then remove the part of the maxilla 



