We were able to identify distinct anterior, medial, posterior (now called Tectal gray) and olivary pretectal nuclei as well as a nucleus of the optic tract, all with largely similar topographical and chemoarchitectonic features to the homologous regions in therian mammals. 
We determined (1) absolute and relative size of the brain, major parts of the brain, the tectum and Tectal gray matter, (2) nerve cell size and density, and (3) the number of cells within the visual and visuomotor centers (thalamus, tectum/praetectum and tegmentum).
Fibres from LPO were observed in the Tectal gray, substantia nigra, area ventralis tegmentalis of Tsai, and the adjacent nucleus mesencephalicus profundus.
Other retinorecipient areas exhibiting substantial decreases (60%) in 2-[ 125I]-iodomelatonin-binding included the optic tectum, lateroventral and dorsolateral geniculate nuclei and Tectal gray area contralateral to the lesion.
Retinal projections to the hypothalamus, dorsalateral anterior thalamus (rostralateral part, magnocellular part, and lateral part), lateral anterior thalamus, lateroventral geniculate nucleus, lateral geniculate intercalated nuclei (rostral and caudal parts), ventrolateral thalamus, superficial synencephalic nucleus, external nucleus, Tectal gray, diffuse pretectal area, pretectal optic area, ectomammillary nucleus, and optic tectum were revealed.
Independent of the extension and cytoarchitecture of the grafts, in all cases numerous transplanted quail cells were observed beyond the limits of the graft spreading along the optic tract, into all the retino-recipient diencephalic nuclei and into the mesencephalic Tectal gray.
In the pretectum, cholinergic fibers innervated the nucleus lentiformis mesencephali and the Tectal gray.
In the accompanying paper we identified these nuclei in the pigeon as the nucleus lentiformis mesencephali--pars lateralis and pars medialis, the Tectal gray, the area pretectalis, and pretectalis diffusus. The Tectal gray has predominantly ascending projections to the diencephalon. The Tectal gray also projects topographically to layers 4 and 8-13 of the optic tectum.
We have found that three pretectal nuclei--the nucleus lentiformis mesencephali, Tectal gray, and the area pretectalis--received heavy retinal input. We have termed them "lentiformis mesencephali, pars medialis" and "lentiformis mesencephali, pars lateralis." The Tectal gray can be divided into a rostral, retinorecipient region and a narrow, caudal, nonretinorecipient region. Separate retinal representations were present in lentiformis mesencephali, pars medialis, lentiformis mesencephali, pars lateralis, the Tectal gray, area pretectalis, and pretectalis diffusus. Only in the lentiformis mesencephali, pars medialis, lentiformis mesencephali, pars lateralis, and the Tectal gray could the retinal representations be analyzed. Whereas the retinal representations in the lentiformis mesencephali, pars medialis and the Tectal gray are comparable, the retinal representation in the lentiformis mesencephali, pars lateralis is different, being a mirror-image mediolaterally.
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