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FEBio implements a 10-node quadratic tetrahedral element. It has four corner nodes and six nodes located at the midpoint of the edges. The shape functions in terms area coordinates are given below. The area coordinates relate to the isoparametric coordinates as follows. $$\begin{equation} \begin{aligned}t_{1} & =1-r-s-t\\ t_{2} & =r\\ t_{3} & =s\\ t_{4} & =t \end{aligned} \,.\label{eq378} \end{equation}$$ The shape functions follow. $$\begin{equation} \begin{aligned}H_{i} & =t_{i}\left(2t_{i}-1\right),\,i=1\cdots4\\ H_{5} & =4t_{1}t_{2}\\ H_{6} & =4t_{2}t_{3}\\ H_{7} & =4t_{3}t_{1}\\ H_{8} & =4t_{1}t_{4}\\ H_{9} & =4t_{2}t_{4}\\ H_{10} & =4t_{3}t_{4} \end{aligned} \,.\label{eq379} \end{equation}$$ The following integration rules are implemented for this element type.