头尾轴

每个动物胚胎一般都有头、尾端，左、右侧和背腹面。从头到尾的轴，称头尾轴。垂直头尾轴的切面为横切面。从左侧到右侧的轴，称左右轴。垂直左右轴的切面为纵切面。从背面到腹面的轴，称背腹轴。垂直背腹轴的切面为额切面。

• inchworm
• incisor
• inclination
• inclination，magnetic
• inclined plane
• inclosure
• incomes policy
• income tax
• Income Tax Amendment
• incunabula
• Independants，Salon des
• Independence
• Independence Hall
• Independence，American War of
• Independence，Declaration of
• Independenee Day
• Independents
• Independent Treasury System
• independent variable
• indeterminacy principle
• Index
• index
• indexation
• index fossil
• Index Librorum Prohibitorum