MESENCEPHALIC ROOT 185 



auriculotemporal division is entirely sensory, and the mandibular 

 nerve proper is nearly all sensory, save a few motor fibers going 

 to the mylohyoid and digastric muscles. The cell bodies from 

 the fibers of the ophthalmic and maxillary divisions of the tri- 

 geminus, apparently, form the dorsal and median portion of the 

 semilunar ganglion, and their central processes the dorsal portion 

 of the sensory root, while the ventral and lateral cells in the semi- 

 lunar ganglion have their central processes in the ventral part of 

 the sensory root and their peripheral processes in the mandibular 

 nerve. Close to its exit from the pons the trigeminal motor root is 

 median to the sensory root, but gradually becomes ventral to it as 

 it approaches the semilunar ganglion and passes through the ven- 

 tral part of the semilunar ganglion. In the ganglion the motor 

 root is separated from the cells and sensory fibers by a connec- 

 tive-tissue sheath (fig. 21, C.T.). The motor and sensory roots 

 (fig. 28, M.R.V. and S.R.V.), while enclosed in a similar con- 

 nective-tissue sheath, are not separated by connective tissue, and 

 still there is no exchange of fibers between the two roots. 

 The nervus trochlearis (fig. 20, IV) will be found in the 

 connective-tissue sheath surroundmg the two trigeminal roots. 



2. Experiments 



In these experiments it was required to sever the mesen- 

 cephalic root at some point caudal to the inferior colliculus, 

 without injuring in any way the trigeminal motor nucleus, roots, 

 or nerves. The same general mode of procedure was applied 

 in these experiments as was used in the first experiments of 

 severing the trigeminal roots. The animals were allowed to live 

 for the same length of time after the operation, and the brains 

 were treated and sectioned serially after the same manner. 



To be absolutely sure of my anatomical relationships, I re- 

 moved the dorsal right half of the cranial wall from a formalin 

 preserved specimen' of about the same size as was to be used in 

 the experiments. A median sagittal section was made thi'ough 

 the brain with a sharp knife and the right half of the brain was 

 completely removed, leaving the left half intact. This prepa- 



