Fig. 3.

a–g. The embryonic motorneurons, their central and peripheral projections, and their target muscles. Theleft column shows individual but representative tracings of single motorneurons (therefore, dimensions of nerve cords and motorneurons may vary slightly between panels), indicating the position of the cell body and dendritic arborizations. Motorneuron names (where they exist) are given at the top left, and the neuroblast of origin (where known) is given at the bottom left (uncertainties are indicated by question marks). The nerve root through which the axon exits the CNS is given at the bottom right (AC, anterior commissure;PC, posterior commissure; ISNa, anterior root of the intersegmental nerve; ISNp, posterior root of the intersegmental nerve; SN, segmental nerve). Thecenter column shows the peripheral projection of the axon and the target muscle(s), which are named according to the nomenclatures of Bate (1993), and in parentheses,Crossley (1978). The right column shows the NMJ in more detail and indicates the peripheral nerve branch through which the motor axon projects (bottom right). We have been unable to show conclusively that muscles VA1 and VA2 are innervated by distinct motorneurons, but on the basis of the number of motorneurons projecting through the SN according to Sink and Whitington (1991a), we propose that they are. To indicate that we are uncertain about which of the dorsal and lateral muscles are innervated by VUM neurons, we have differentially highlighted those muscles that we think are the most likely targets, in agreement with Sink and Whitington (1991a).n = sample size for each labeled neuron.