400 THE VERTEBRATE SKELETON. 



a. The most anterior of these nerves, the olfactory, leaves 

 the skull by a number of small holes piercing the cribriform 

 plate (fig. 72, 5). 



6. The second, or optic, passes out by a large hole, the 

 optic foramen (fig. 75, II) piercing the orbitosphenoid. The 

 optic foramen is the most anterior of the three prominent 

 holes seen within and immediately behind the orbit. 



c. The third, fourth, and sixth nerves, i.e. those supplying 

 the eye muscles, and with them the first or ophthalmic branch 

 of the large fifth or trigeminal nerve, pass out by a large hole, 

 the foramen lacerum anterius (fig. 75, III, IY, V^VI), 

 which, as has been already mentioned, lies between the 

 orbitosphenoid and alisphenoid. 



d. Immediately behind the foramen lacerum anterius, the 

 alisphenoid is perforated by a prominent round hole, the 

 foramen rotundum (fig. 75, V 2 ), through which the second 

 branch of the trigeminal nerve passes out. 



e. A quarter of an inch further back there is another 

 prominent hole, the foramen ovale (fig. 75, Y 3 ), through 

 which the third branch of the trigeminal nerve leaves the 

 cranium. 



f. The seventh or facial nerve, as already mentioned, 

 leaves the cranial cavity and enters the auditory capsule, 

 through an opening in the periotic called the internal 

 auditory meatus, while it finally leaves the skull by the 

 stylomastoid foramen (fig. 75, VII), which lies between 

 the tympanic bulla, the paroccipital process, and the mastoid 

 portion of the periotic. 



g. The eighth or auditory nerve on leaving the cranial 

 cavity, passes with the facial straight into the auditory capsule 

 through the internal auditory meatus (fig. 72, 20). It is 

 then distributed to the organ of hearing. 



h. The ninth, tenth and eleventh nerves leave the skull 



