The answer is very close to “a”. The “cradle” on a neuronal cell that embraces another is often a location that sends out neuro-transmitter (some kind of chemicals that mediate the information exchange) into the next. If it’s the case, we consider the two neurons to be “connected” to each other. The connection (transmitter + receiver) between them is called as a “synapse”. The cradle on the pre-synaptic side is sometimes called as a “bouton” (button in French). Sometimes, the strand (or the “dendrite” as it is usually called) on the post-synaptic side turns out to be short, thus called “spine”.
But, we should be careful in saying these too confidently. There are too many variations and exceptions in nature. Not all the cradles are boutons – they cannot be decided solely by their shapes. Not all synapses involve boutons or spines – sometimes boutons embrace in the middle of a long branch to make a synapse. so on and so on.
So we may say that what we are seeing here is a putative synapse.
Thanks for the great question.