ORIGIN OF JAW APPARATUS 391 
35 indicates, the fibers of the mandibular nerve are made up into 
discrete bundles very soon after leaving the brain, which are 
destined for distinct peripheral structures and run out to them 
without further complications; 1.e., its main branchings occur 
close to its origin. 
From the foregoing sketch of the maxillary and mandibular 
nerve trunks it is quite apparent that these nerves were present 
long before the dentigerous jaws arose out of the Amphioxine 
jaw apparatus and that they have been gradually transformed, 
as the jaw apparatus evolved, into the characteristic nerves 
of the maxillary and mandibular mechanisms of the higher verte- 
brates, gradually assuming the condition and appearance of 
nerves devoted almost exclusively to these important structures. 
In Bdellostoma, as the mandibular mechanism has already been 
established and the maxillary mechanism is still undifferenti- 
ated, the nerves of the former show greater specialization for 
the control of a motor mechanism than does the maxillary nerve. 
Neither the maxillary nor the mandibular nerves are new 
branches of old nerves, they are segmental trunks more ancient 
than definitive gnathastome jaws. 
The fifth member of the trigeminal complex is the so-called 
seventh of vertebrate anatomy otherwise known as the N. faci- 
alis. It connects with the lateral border of the medulla a short 
distance behind the group-of four which leave the tip. After 
viewing the crowded condition of the roots on the tip of the 
medulla this interspace, bare of nerve trunks, is noticeable. 
The manner of connection of the VII roots with the edge of the 
medulla varies. Sometimes it appears as a single trunk; usually 
it shows two roots, one motor root from the ventral edge of the 
medulla and an acoustic root more dorsal. Occasionally a 
third fine strand of fibers leaves the medulla cephalad of the 
motor root and runs out some distance before it joins the nerve 
trunk. However, these two or occasionally three external 
roots do not indicate the internal complexity of its make-up. 
Into its root enter fibers from six sources. 
Its peripheral course is outward and backward around the 
auditory capsule, as though. the latter by growing forward had 
