In order to characterize each nucleus of the interpeduncular complex; the central nucleus (IPC), the paramedian nucleus (IPC), the outer division of the posterior nucleus (IPO), the inner division of the posterior nucleus (IPI), and the apical nucleus (IPA), the efferent fiber connections from these nuclei were examined both by Fink-Heimer's method and by the retrograde transport of horseradish peroxidase (HRP) using cats.
The efferent fibers from the IPC and IPP projected to the dorsal tegmental nucleus of Gudden via the pedunculotegmental tract and to the mediodorsal nucleus of the thalamus via the fasciculus retroflexus. The IPO projected to the ventral tegmental nucleus of Gudden via the pedunculotegmental tract, and projected to the anterior mamillary nucleus, the lateral hypothalamic nucleus, the preoptic area, the diagonal band of Broca and the septal area via the medial forebrain bundle. The IPA projected to the anterior mamillary nucleus, the lateral hypothalmic nucleus and the preoptic area.
Based on these results, the interpeduncular complex may be divided into a central group including the IPC and IPP, and a posterior group including the IPI, IPO and IPA.

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1) The author established the representation of the lower motor center of all the extrinsic ocular muscles by means of HRP labeling in the rat.2) The muscles which are supplied by the neurons on both sides of the oculomotor nuclei are the levator palpebrae superioris, superior rectus, medial rectus, inferior oblique, inferior rectus, superior oblique and lateral rectus.3) The muscles which are supplied by the neurons on both sides of the trochlear nuclei are the levator palpebrae superioris, inferior rectus and superior oblique.4) The muscles which are supplied by the neurons on both sides of the abducens nuclei are the levator palpebrae superioris, superior rectus and lateral rectus, while lightly stained neurons were observed in specimens from the inferior oblique, inferior rectus and superior oblique.5) The inferior oblique showed a few neurons originating in the contralateral trochlear nucleus but none in the ipsilateral. The lateral rectus revealed its originating neurons mostly in the ipsilateral abducens nucleus.6) Although it is true that a lower motor center for each muscle does exist, our results indicate that there can be no lower motor center consisting of originating neurons which supply only one muscle in the rat.

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1) Studies were made of the accessory abducens nucleus and its relationship to the extraocular muscles besides the retractor bulbi muscles in the rat.
2) All the extraocular muscles had nerve fiber connections from the accessory abducens nucleus besides the retractor bulbi muscles.
3) The relationship between the accessory facial nucleus and accessory abducens nucleus was investigated. The accessory facial nucleus was located from dorsal of the principal facial nucleus to the medial proximal part of the descending part of the facial root fibers, while the accessory abducens nucleus was located from the medial distal part to the descending part of the facial root fibers.

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A new method of embedding with GMA, Quetol 523 and methyl methacrylate for light and electron microscopic observation of semi-thin sections was devised for easy embedding, infiltration, sectioning and staining. The method employed purified GMA (glycol methacrylate), Quetol 523 and methyl methacrylate with QCU-1 (2,2'-azobis isobutyronitrile paste) as a catalyst. A mixture of these materials could be polymerized at 60°C for about 12 hr to produce a bloek with excellent cutting properties.
Tissues were fixed in 2.5% glutaraldehyde with buffered phosphate at pH 7.4 for 3hr or 2% glutaraldehyde-4% paraformaldehyde with buffered phosphate at pH 7.4 for 3hr. Seetions 0.2-0.5μm thick were cut with glass knives using troughs on a conventional ultramicrotome. They could be attached to slide glasses or grids by water flotation, without adhesive. They should be dried at room temperature. Staining with aqueous solutions of basic and acid dyes, without removal of the embedding matrix, was sharp and brillant as usual. These stained sections were observed under a light microscope. Identical sites on such sections,0.2-0.3μm thick, could be examined with an accelerating potential of 100 kV at low magnification (250-1,500 times) using an LEM-2000 combined light and electron microscope. Thus, photomicrographs and electron micrographs of identical sites on tissue samples could be compared exactly.
The resolution of the electron microscope was so high that the cytoplasmic components were readily identified in the cytoplasm. Osmium tetroxide vapor staining gave better contrast in the images of the specimens.

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