PLATE 4 



EXPLANATION OF FIGURES 



18 Left half of a section twenty-one sections cephalad of figure 17 (ex. 64), 

 passing through the caudal end of the inferior colliculus (corpora quadrigemina). 

 Observe that the lesion (Les.) has completely severed the mesencephalic root 

 at this level. As in the previous section, the degenerated descending mesen- 

 cephalic root fibers appear in two places : 1) opposite the aquseductus cerebri im- 

 mediately lateral to the central gray, and 2) intermingled with the trigeminal 

 motor fibers, which are approaching the trigeminal sensory root directly median 

 to the trigeminal sensory nucleus (substantia gelatinosa). X 8. 



19 Similar view to figure 18, but from a section fifty- two sections cephalad 

 through the cephalic end of the inferior colliculus. This section is above the 

 lesion, so that the few degenerated fibers shown in the mesencephalic root opposite 

 the aquseductus cerebri are ascending fibers having their cell bodies in the 

 semilunar ganglion. The trigeminal motor root, which consists of about one- 

 fifth descending mesencephalic root fibers taking origin from cells in the 

 mesencephalon and locus cceruleus, now occupies a position directly median to 

 the trigeminal sensory root. There is no connective-tissue sheath separating these 

 two roots, but they are sharply marked off, absolutely no intermingling of fibers. 

 See also figures 11, 20, and 28. X 8. 



20 Tranverse section through the left trigeminal roots (lesion side) from 

 the same series as figures 14 to 19 (ex. 64), about half way between the exit of the 

 trigeminal motor root and the semilunar ganglion, and sufficiently magnified so 

 that each degenerated medullary sheath of any size could be accurately sketched. 

 Observe that by far the greater part of the trigeminal root is sensory and con- 

 tains no more degenerated fibers than would be found in a section of a normal 

 root, that the motor root is mainly ventral to the sensory, the line of separation 

 being sharply marked, and about one-fifth of its fibers are degenerated 

 mesencephalic root fibers taking origin from cells in the mesencephalon and 

 locus coeruleus. Note that the trochlear nerve in the sheath surrounding the 

 trigeminal roots contains many degenerated fibers. It was undoubtedly severed 

 in this experiment. X 24. 



21 Transverse section through the semilunar ganglion from the same series 

 as the previous figures (ex. 64). Observe the trigeminal motor root, containing 

 degenerated descending mesencephalic root fibers, passing through the ventral 

 portion of the ganglion and separated from the ganglion by a connective-tissue 

 sheath. There are no more degenerated fibers in this ganglion than would 

 occur in any normal ganglion. X 12. 



22 Transverse section through the various trigeminal nerves a little periph- 

 eral to the semilunar ganglion from the same series as the preceding drawings 

 (ex. 64) . To the right will be seen two entirely sensory nerve trunks, ophthalmic 

 and maxillary, in which there are no degenerated descending mesencephalic root 

 fibers. To the left the mandibular nerve will be seen to have separated into 

 three portions: 1) The nervus auriculotemporalis, which is purely sensory and 

 contains no degenerated descending mesencephalic root fibers. 2) The N. mandi- 

 bularis proper, which with the exception of a few motor fibers for the mylohyoid 

 and digastric muscles is sensory and contains no degenerated descending mesen- 

 cephalic root fibers. 3) Each of the motor portions of the N. masticatorius, 

 namely, the N. massetericus, N. pterygoideus, and N. temporalis profundus, 

 contains numerous degenerated descending mesencephalic root fibers, while 

 the N. buccinatorius, which is entirely sensory, contains none. X 8. 



210 • 



