392 



ANATOMY IN A NUTSHELL. 



The sixth nerve or Abducent has its superficial origin from the lower part 

 of the pons in the groove between the pyramid and the pons or in the constricted 

 part of the pyramid. Its deep origin is in the floor of the fourth ventricle 

 close to the median line and a little lower than that of the motor root of the 

 fifth. This origin is traced to a nucleus under the upper half of the funiculus 

 teres. This nerve enters the cavernous sinus after the dura mater of the basilar 

 process of the sphenoid, running through a notch immediately below the pos 

 terior clinoid process. In the cavernous sinus it lies external to the internal 

 carotid artery. From this sinus it enters the orbit between the two heads of 

 the External rectus to supply this muscle, entering the muscle on the orbital 

 surface. 



PLATE CCVII. 



SUP. RECTUS. 



INTERNAL RECTUS. 



INf. OBLIQUE. 



EXTERNAL RECTUS. 



SUP. -OBLIQUE. 



INF. RECTUS. 'y 



Showing the Directions that Muscles of the Eye-Ball Move the Eye. 



For its position in the sinus (See Plate CCXXXII.) All the structures on 

 the floor of the sphenoidal fissure lie between the two heads of the External 

 rectus. For position of the nerves in the orbit (See Plate CCXV). The 

 fourth nerve lies on the Superior oblique, the frontal nerve on the Levator pal- 

 pebrae, and the lachrymal nerve on the External rectus. The superior division 

 of the third nerve lies along the Superior rectus; the nasal nerve crosses the optic 

 nerve from without inward: the optic nerve is surrounded anteriorly by the 

 ciliary nerves; the lenticular ganglion lies between the optic nerve and the Ex- 

 ternal rectus. The sixth nerve is on the outer surface of the orbit. The in- 

 ferior division of the third nerve is below the lenticular ganglion and this nerve 

 is joined by filaments from the cavernous plexus, carotid plexus, and the ophthal- 

 mic nerve. If the sixth nerve is paralyzed internal or convergent squint 

 follows as the External rectus loses its function. The pupil is contracted to 

 some extent in paralysis of this nerve as some of the sympathetic fibers to the 

 radiating muscle of the iris pass along this nerve. 



The fifth nerve is the largest of the cranial nerves. It is more like a spinal 

 nerve than any other of the cranial nerves. It is a compound nerve, having 



