Picture from Dixon SJ et al. (2005) Development "Muscle arm development in Caenorhabditis elegans."

Figure 1. The muscle arms of C. elegans. (A) An illustration of the BWMs (red) of the left side of C. elegans. Each BWM quadrant is organized into two rows. (B) A cross-section of A adapted, with permission, from White et al. (White et al., 1986). Each muscle of the two dorsal BWM quadrants and each muscle of the two ventral quadrants (red) extends arms to the nearest nerve cord (dark green) in either the DHR or the VHR, respectively. Only the muscle arms of the ventral left quadrant are indicated by green arrows. The LHR is indicated. (C) A transmission electron micrograph by John White (with permission) of the boxed region in B. BWMs are shaded pink. (D) The dorsal right (top) and dorsal left (bottom) BWMs that express MB::YFP from the trIs30 integrated transgene in a young adult. The Cpppaaa BWM is indicated (yellow arrow), along with four muscle arms (green arrows). (E) The ventral left (top) and ventral right (bottom) BWMs. The red asterisk indicates the position of the vulva. (F,G) Tracings of the dorsal and ventral BWMs, respectively. The identities of the distal muscles that express Mb::YFP at high levels are bright yellow, and those that express Mb::YFP at lower levels are light yellow. The head BWMs are shaded in dark grey, while the neck BWMs are shaded in light grey. The black X' in (G) represents the vulval muscles, which do not express Mb::YFP from trIs30 transgene. Anterior is to the left in all panels except in B and C. Scale bars: 50 μm. DHR, dorsal hypodermal ridge; LHR, lateral hypodermal ridge; VHR, ventral hypodermal ridge.