Fig. 1. Transverse secti ons through the posterior thalamus to show the para geniculate nucleus (Pg)in the cat. Nissl stain. x16. The numbers indicate se rial sectional numbers. GLd, dorsal lateral genicu late nucleus; GM, medial geniculate nucleus; LP, posterior lateral nucleus; PA, anterior perigeniculate nucleus; PL, lateral pul vinar nucleus; R, thalamic reticular nucleus; Sg, sup rageniculate nucleus.

Fig. 2. Transverse secti ons through the posterior thalamus to show the para geniculate nucleus in the racoon dog (Nyctereutes procyonoides viverrinus Temminck et Schlegel). Nissl stain. x17. Abbrevia tions see Fig. 1.

Fig. 3. Transverse sec tions through the posterior thalamus to show the pa rageniculate nucleus in the bear (Ursus thibetanus ja ponicus Schlegel). Nissl stain. x10. Abbreviations see Fig. 1.

1. Berman, N. and Jones, E. G.: A retino-pulvinar projections in the cat. Brain Res. 134, 237-248, 1977. 2. Guillery, R. W.: The laminar distribution of retinal fibers in the dorsal lateral geniculate nucleus of the cat: a new interpretation. J. comp. Neurol. 138, 339-367, 1970. 3. Hirokawa, S.; Ueber die Thalamuskerne der katze. Jpn. J. Med. Sci. Part I. Anat. 9, 119-147, 1941. 4. Hollander, H. and Venegas, H.: The projection from the lateral geniculate nucleus onto the visual cor tex in the cat. A quantitative study with horseradish peroxidase. J. comp. Neurol. 173, 519-536, 1977. 6. Jimenez-Castellanos, J.: Thalamus of the cat in Horseley-Clarke coordinates. J. comp. Neurol. 91, 307-339, 1949. 10. Niimi, K. and Kuwahara, E.: The dorsal thalamus of the cat and comparison with monkey and man. J. Hirnforsch. 14, 303-325, 1973. 11. Niimi, K. and Spraque, J. M.: Thalamo-cortical organization of the visual system in the cat. J. comp. Neurol. 138, 219-249, 1970. 12. Niimi, K., Kanaseki, T. and Takimoto, T.: The comparative anatomy of the ventral nucleus of the la teral geniculate body in mammals. J. comp. Neurol. 121, 313-324, 1963. 13. Niimi, K., Matsuoka, H., Yamawaki, M. and Matsumoto, H.: Thalamic afferents to the visual cortex in the cat studied by retrograde axonal transport of horseradish peroxidase. Brain Behav. Evol. 1980, (in press). 14. Rioch, D. McK.: Studies on the diencephalon of carnivora. Part. I. The nuclear configuration of the thalamus, epithalamus, and hypothalamus of the dog and cat. J. comp. Neurol. 49, 1-119, 1929. 15. Thuma, B. D.: Studies on the diencephalon of the cat. I. The cytoarchitecture of the corpus geniculatum laterale. J. comp. Neurol. 46, 193-199, 1928.

The parageniculate nucleus in carnivores Masaomi YAMAWAKI, Yasutaka OKADA, Toshio AISAKA and Kahee NIIMI Third Department of Anatomy, Okayama University Medical School, Okayama, Japan The present study attempts to study the comparative anatomy of the parageniculate nucleus in carnivores. In Felidae it is closely applied to the lateral margins of the posterior lateral and suprageniculate nuclei, and is composed of small, deeply stained and fusiform cells. Caudally it lies just lateral to the ventrolateral part of the lateral pulvinar nucleus and to the suprageniculate nucleus. As the dorsal lateral geniculate nucleus appears, the paragenicu late nucleus extends ventrally between the dorsal lateral geniculate nucleus and the supragenicu late nucleus or the inferior pulvinar nucleus. In the other carnivores examined, the paragenicu late nucleus tends to be confined to the lateral margins of the lateral pulvinar and supragenicu late nuclei. At the most anterior levels of the dorsal lateral geniculate nucleus, the paragenicu late nucleus extends ventrolaterally to reach the region just dorsomedial to the dorsal lateral geniculate nucleus, but does not extend between the geniculate nucleus and the dorsal thalamus proper. The parageniculate nucleus is regarded as a connecting cell group between the dorsal lateral geniculate nucleus and the dorsal thalamus proper, and may be a dorsal thalamic de rivative.