DISSECTION OF THE SHARK 31 



III. N. oculomotorius. From the floor of the midbrain 

 to mm. obliquus inferior and rectus superior, inferior, and 

 medialis. 



IV. N. trochlearis. From the roof of the midbrain to m. 

 obliquus superior. 



VI. N. abducens. From the floor of the medulla oblongata 

 to m. rectus lateralis. 



V and VII. The trigeminus and facialis nerves are so inti- 

 mately united that microscopic methods are required for their 

 separation. In Figs. 2 and 3 they are drawn very diagram- 

 matically after slight dissection and separation of the roots and 

 ganglia. Their true composition is shown in Fig. 5. The two 

 upper (more rostral) roots of the complex are the sensory and 

 motor V; the lower ones belong to VII. The sensory V root 

 receives its fibers from the skin of the whole head in front of 

 the gill region. The motor V root supplies the jaw muscles; 

 the motor VII root those of the hyoid arch. The sensory VII 

 root (nervus intermedius, or portio intermedia of Wrisberg) 

 receives most of its fibers from taste-buds and the mucous 

 lining of the mouth. The lateral line roots which enter the 

 brain in front of the ear are usually named as parts of the VII 

 nerve; see Section 18. 



VIII. N. acusticus. From the labyrinth of the ear to the 

 acoustico-lateral area of the medulla oblongata. The cochlear 

 ramus is absent or rudimentary. A small sensory spot in the 

 saccule, the lagena, is regarded as the organ from which the 

 cochlear sense organ (spiral organ) of mammals has been differ- 

 entiated; its nerve, accordingly, is homologous with the 

 cochlear nerve of man. 



IX. N. glossopharyngeus. Arises from the oblongata by 

 three roots, two sensory and one motor, passes under the mem- 

 branous labyrinth of the ear and forks around the first gill cleft. 

 It contains visceral sensory and visceral motor fibers for the 

 innervation of the first gill and also a small lateral line com- 

 ponent (r. supratemporalis IX, Figs. 4 and 5). 



X. N. vagus. Arises from the oblongata by several roots 

 which form a large trunk from which arise branchial rami to 

 fork around the second to fifth gill clefts (visceral motor and 

 visceral sensory); also r. visceralis vagi for the viscera of the 



