Does bouton morphology optimize axon length?

The total length of cortical axons could be reduced if the parent axons maintained straight trajectories and simply connected to dendritic shafts via spine-like terminaux boutons and to dendritic spines via bead-like en passant boutons. Cortical axons from cat area 17 were reconstructed from serial electron micrographs and their bouton morphology was correlated with their synaptic targets. En passant or terminaux boutons did not differ in the proportion of synapses they formed with dendritic spines and shafts, and thus, the two morphological variants of synaptic bouton do not contribute directly to optimizing axon length.