The mouse hypoglossal nuclei in the normal state and after unilateral hypoglossal neurectomy as well as the mouse hypoglossal nerves severed or ligated were examined with the electron microscope.
The normal hypoglossal neurons were classified into two types, dark and light cells; the former shows the developed lamellar granular ER, a withered contour of the cytoplasm and an electronopaque nucleus with a folded nuclear envelope, while the latter has poorly dispersed granular ER, a swollen, smooth contour of the cytoplasm and an electron-transparent nucleus with a smooth, expanded nuclear envelope. There are various intermediate forms between these two representative types.
The main changes seen in hypoglossal nerve cells after neurectomy are as follows.
(1) The cisterns of the granular ER are seen swollen from the 3rd day till the 14th day after neurectomy. The granular ER is dispersed into isolated cisterns and loses the original collected pattern. The density of distribution of RNP particles becomes lower. This appearance corresponds to the dustlike Nisslbodies and the paler cytoplasmic figure observed with Nisslstaining in the period of maximal retrograde chromatolysis. The fresh production of the granular ER is mainly carried out by the elevation of tubular extensions of the outer nuclear membrane studded with RNP particles. Afer the peak of chromatolysis the granular ER recovers the original compact pattern.
(2) The increase in number of the neurofilaments, the thin and thick filaments, especially of the former, is seen throughout the entire cytoplasm from the 3rd day till the 14th day after neurectomy. This change is more remarkable in dark cells with the swollen granular ER cisterns. These new thin filaments are created in the granular ER. The thick filaments are formed by elongation of the small Golgi vacuoles, the Golgi vesicles and the thin membranes encircling the granular ER cisterns. The new formation of the thin and thick filaments can be more clearly observed in the axon-hillock region. In this region the thick filaments are mainly produced from the irregular vesicles which derive from the granular ER and the vesicles and small vacuoles of the Golgi apparatus.
(3) The nuclear envelopes of light cells become folded. The nuclei of some dark cells swell to assume the smooth expanded contour and show the paler nucleoplasm. In the later period of retrograde chromatolysis, they become darker and wither again. The masses of fine granules in the nucleus attach to the inner nuclear membrane and the same fine granules sometimes exist within the nuclear pores. This suggests the migration of nuclear substances to the cytoplasm.
(4) The Golgi vacuoles swell in the earlier period of chromatolysis. The paired Golgi membranes decrease in number, while the Golgi vesicles increase in number and disperse to the cytoplasm. the Golgi vesicles increase in number and disperse to the cytoplasm. The Golgi apparatus seem to originate from the agglomeration of the vesicles budded from the tubular extensions of the outer nuclear membrane not studded with RNP particles. In the later period of chromatolysis, the Golgi apparatus recover their original compact pattern.
(5) The mitochondria show swelling, shrinkage and disintegration of the cristae mitochondriales. The small mitochondria increase in number 1 week after neurectomy.
In the central stump of the severed hypoglossal nerve and the portion immediately proximal to the ligature in the hypoglossal nerve, numerous unmyelinated nerve axons are newly grown. They contain rich thin filaments, sparse thick filaments, mitochondria and irregular vesicles. In the portion immediately distal to the ligature in the same nerve, all the myelinated nerve fibers fall into complete degeneration.
The present findings indicate that the newly-formed thin and thick filaments in the nerve cell body are transported, together with the mitochondria and the irregular vesicles originating

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The brains with the optic nerves of 25 mice were impregnated with silver at intervals up to 125 days following either unilateral or bilateral enucleation of the eyeballs for investigation of efferent fibers in the optic system. Serial sections were examined in every case for axonal degeneration in the optic pathway. Results obtained were as follows:
1. The optic nerve of the mouse consists mainly of fibers of retinal origin, but also contains a small number of efferent fibers.
2. All the retinal fibers completely decussate in the optic chiasma there are no uncrossed retinal fibers.
3. The efferent fibers originate partly in the superior colliculus and partly in the lateral geniculate body.
4. The efferent fibers completely cross at the optic chiasma and run to the retina of the opposite eye passing through the optic nerve. There are no uncrossed efferent fibers in the mouse optic system.

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To discuss and compare the a u thor's results with previous authors' the problem is divided into six items: Arteria or Ramus angularis oris; continuation of A. facialis; branching features of Aa. infraorbitalis and labialis superior; courses; and branches of the arteries; anastomosis between the superior labials on both sides. The present author wishes to give new names for some branches.

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