- 1 The umbilical cords of the cow, rabbit, guinea-pig and sheep possess a sphincter muscle in the umbilical ring. These cords all enter the abdomen of the foetus at a right angle.
- 2 The umbilical cords of the rat, dog, cat and man make an acute-angled entry into the abdomen and have no umbilical sphincter. The pangolin and the macaque also fail to develop a sphincter muscle in the umbilical cord.
- 3 The structure of the sphincter is described and some possible functions are discussed.