Figure 5: (a) Ultrastructure of sperm from a patient with fibrous sheath dysplasia. Nucleus (n), acrosomal vesicle (AV), segmented columns (SC), proximal centriole (*), mitochondria (mi), and outer dense fibers (ODF). Note the absence of the annulus and the invasion of the midpiece by marked hypertrophy and hyperplasia of the fibrous sheath (FS). (b) Ultrastructure of sperm from a patient with situs inversus. Distal principal piece (PP): axoneme and FS. The 9 peripheral doublets (d) and the radial spokes (green line), the 2 single central microtubules (c), the central bridge (red line) and the fibrilar sheath (dashed circle) are intact. Note the absence of dynein arms (dashed pink lines) and of nexin bridges (dashed blue line), the doublet indicated by a perpendicular line (dotted line) to the central microtubules is named N°.1 with the following numbering in the clockwise direction.