14 brains of Globicephala sp.and 3 brains of Neomeries sp.were collectedand fixed with 10% formalin.The brains were examined macroscopically,and the eye muscle nerves were severed,sectioned and stained with Nissl'smethod in order to observe their minute structures.Among 22 trochlear nerves of Globichephala sp.examined,14 cases showedconspicuous detectable ganglion,about 1—2mm in diameter.But none wasfound along the nerves of Neomeris sp.In 9 cases,2 or more roots are revealed.The roots are arranged antero-posteriorly,but turned dorsoventrally a short distance after their emergence.There are 4 cases in which ganglion has been found along the dorsal root.No ganglion is detectable along the oculomotor or abducent nerves eitherin Globicephala sp.or in Neomeris sp.intracranially,however,individualcells were found scattered among the nerves fibers.There are over 40 cellsin a single section of the trochlear ganglion.Sometimes it reaches to morethan 250 cells in a single section.The cells found in the Nissl preparationsare quite uniform in appearance,about 30—40? in diameter.The Nissl bodyis fine and evenly distributed,the cells are capsulated.The result obtainedfrom Cajal's method was poor,probably due to prolonged fixation and tech-nical error.Very few of them are uni- or multipolar in appearance.How-ever,it is not conclusive.No trochlear ganglion was found in Neomeris sp.Apparently trochlearganglion may not be present in every species of cetacea.The nature of trochlear ganglion has been briefly discussed.Furtherstudy is needed in order to prove whether the ganglion is sensory or auto-nomic.