THE NERVOUS SYSTEM 1 23 



The next important branch is the anterior auricular n. which 

 passes to the muscles of the craniolateral side of the ear. The 

 seventh nerve separates into three main branches, near the 

 caudal margin of the masseter muscle and passes directly 

 toward the cornor of the mouth. Near the cranial border of 

 the masseter muscle all three branches break up into a plexus 

 of small nerves which are distributed to the muscles of the 

 vibrissae, upper and lower lips, and in short to the skin and 

 superficial structures of the entire face craniad to the orbit and 

 masseter muscle and a large nerve to the region of the snout. 

 Numerous small fibers pass from the larger nerves to the 

 integument and other structures. The facial nerve, as the 

 name implies, innervates most of the superficial structures of 

 the entire facial region. 



Method: Beginning just ventrad of the zygomatic arch very 

 carefully clear the subcutaneous muscle and superficial fascia 

 toward the ear and toward the mouth until a white cord (part of 

 the VII nerve) , which extends in a straight line from under the 

 parotid gland over the masseter muscle toward the cornor of 

 the mouth, but divides into numerous fibers just before reaching 

 the cranial margin of the masseter muscle, is located. Follow 

 this cord and verify the above description of the seventh 

 cranial nerve and its principal branches. After the root of 

 the facial nerve and posterior and anterior auricular branches 

 have been exposed, it is a good plan to slit the craniolateral 

 wall of the external auditory meatus open as far as its entrance 

 into the cochlea (Fig. 2, EA), in order to facilitate locating the 

 sylomastoid foramen by probing. Great care must be used 

 to prevent cutting the seventh nerve or one of its auricular 

 branches. 



The trigeminal (trigeminus, trifacial, V cranial) nerve 

 arises from the pons Varolii by two roots, a large sensory root, 

 which enlarges to form the semilunar (Gasserian) ganglion 

 from which three branches (a. mandibular or third, b. max- 

 illary or second and c. ophthalmic or first) arise and pass out 

 of the cranium through three different foramina. The second 



