PLATE 6 



EXPLANATION OF FIGURES 



28 to 30 are from another series of a guinea-pig's brain stem, including the 

 trigeminal roots, semilunar ganglion and trigeminal nerves. In this experiment 

 (no. 65) the mesencephalic root was severed in the region of the locus coeruleus 

 above the trigeminal motor nucleus, and the incision extended deeper than was 

 intended so that a part of the motor nucleus was injured. This experiment 

 served as a check for determining absolutely which nerves contained motor 

 fibers. The degenerated fibers were stained after a modified Marchi method. 

 It should be noted that the trigeminal roots were bent outward during the process 

 of fixation so that the trigeminal roots and semilunar ganglion appear in some- 

 what oblique longitudinal section. 



28 Approximately longitudinal section through the trigeminal roots, semi- 

 lunar ganglion and formation of some of the trigeminal nerves (ex. 65). As in 

 the previous series, note the general ventral position of the motor root and its 

 sharp line of demarcation from the sensory root and the semilunar ganglion. 

 Also the presence of many more degenerated medullary sheaths, most of which 

 are trigeminal motor fibers and the balance are descending mesencephalic root 

 fibers. Observe that there are no more degenerated nerves in the sensory root 

 and semilunar ganglion than would occur in a section of any normal semilunar 

 ganglion. Also that no degenerated motor fibers or descending mesencephalic 

 root fibers pass to the semilunar ganglion. X 12. 



29 A more peripheral section from the same series as figure 28. At this 

 level all of the components of the mandibular nerve have appeared, but it is 

 not cephalic enough to show the differentiation of the semilunar ganglion into 

 the ophthalmic and maxillary nerves. Observe that there are no more than the 

 normal number of degenerated medullary sheaths in the serhilunar ganglion, 

 auriculotemporal and buccal nerves,* and that most of the degenerated nerve 

 fibers are found in the masseter, pterygoid, and deep temporal branches of the 

 masticator nerve. They consist of both trigeminal motor fibers and descending 

 mesencephalic root fibers. The few degenerated fibers found in the mandibular 

 nerve proper are trigeminal motor fibers for the mylohyoid and digastric muscles. 

 X 8. 



30 Peripheral section of the nervus massetericus and three of its branches 

 one of which has entered the masseter muscle (ex. 65). This section was suffi- 

 ciently magnified to allow for the accurate drawing of every particle of degener- 

 ated myelin. A comparison with a similar section (ex. 64) shows many more 

 degenerated fibers in the peripheral branches, the increase being trigeminal 

 motor fibers. Also there are as many, if not more, degenerated fibers in the 

 peripheral branches than there were in the main trunk of the masseter nerve, 

 indicating a branching of these fibers. X 32. 



31 to 35 are isolated cells taken from a series of a brain stem and semilunar 

 ganglion of a guinea-pig, stained after a modified Cajal method. All drawings 

 were from the same magnification. 



31 (a) One of the semilunar ganglion cells, which is similar in every respect 

 to a typical spinal ganglion cell, (b) A locus coeruleus cell from the same 

 series. Note identical type of unipolar sensory cell, with the exception of the 

 coiled process. X 66.4. 



(Continued on p. 216) 



214 



I 



