130 NERVOUS SYSTEM OF VERTEBRATES. 



of various nerve trunks. This will be clear from an examination 

 of Figs. 62 and 63. In the former the canals of the head are 

 shown with the nerves which innervate them but without the 

 accompanying components of the other kinds. In Figure 63 the 

 various components which constitute the cranial nerves of Menidia 

 are shown as they are combined in nerve trunks. The neuro- 

 mast components are shown in outline but the canals themselves 

 are omitted on account of the complexity of the figure. The root 

 and ganghon of the lateral Hne nerve is closely related to those 

 of the, vagus, as is nearly always the case. In many fishes also 

 fibers from this root go into the IX nerve in which they run for 

 some distance to reach their sense organs. In Menidia the fibers 

 to the supraorbital canal, forming the ramus ophthalmicus super- 

 facialis YH, run with the general cutaneous fibers which form the 

 ramus ophthalmicus superfaciahs V, the two constituting a supra- 

 orbital trunk. This is the most common arrangement in other 

 fishes also. The fibers for the infraorbital canal in Menidia run' 

 with general cutaneous and general visceral fibers in the maxillary 

 trunk. The fibers to the infraorbital row of sense organs are 

 . known as the ramus buccalis VII and in most fishes are independent 

 of other components for the greater part of their course. The 

 fibers destined to the hyomandibular canal form a component of 

 the ramus hyomandibularis, which contains also general cutaneous, 

 visceral sensory and visceral motor fibers. It will be seen imme- 

 diately that all the neuromast fibers, no matter in what rami they 

 run, have the same central connections as well as the same type 

 of peripheral organs, and are therefore justly considered as a 

 single system of nerve components. The distribution of these 

 components in the cyclostomes (Fig. 51) and in amphibia (Fig. 

 79) should be compared with that in Menidia (Fig. 63). 



Special cutaneous centers. — In the brain of cyclostomes 

 the neuromast fibers are intimately associated with the general 

 cutaneous fibers and end in the same sHghtly specialized centers. 

 (See previous chapter.) In the brain of a selachian or ganoid 

 fish although the general and special cutaneous fibers are still 

 almost as intimately associated, a higher development of the 

 centers has taken place and the special cutaneous fibers end chiefly 



