A less complicated source of neurons suitable for this type of studies is the parasympathetic ciliary ganglion. In the pigeon and in the chick this ganglion is known to contain only two classes of neurons, both of which are cholinoceptive and cholinergic and that innervate the muscle fibres of the choroid plexus of the eye, the sphincter iridis and the ciliary body (Marwitt et al., 1971). The iris and the ciliary muscle in birds are both striated (Ovio, 1927), whereas in the mammal they are smooth. Neurons of the ciliary ganglion of the chick embryo can be cultivated in tissue culture (Hooisma et al., 1975) either in explants of whole ganglia or after dissociation, as individual cells. Branching neurites grow radially from the ganglia. A corona of neurites with a diameter of 500-1000 μm surrounding the ganglia is formed during 2 days in culture. Mixed cultures of ciliary neurons and skeletal-muscle cells have been used for the study of the process of neuron-to-target recognition.