Complex sentence: The dorsal fins have rounded apexes and are placed well back on the body, the first originating behind the midpoints of the small pelvic fins; the first dorsal fin is about twice as high as the second.
Split into simpler sentences: The dorsal fins have rounded apexes and are placed well back on the body, the first originating behind the midpoints of the small pelvic fins. The first dorsal fin is about twice as high as the second.