Limbs very slender; posterior nearly twice the length of the anterior.
3, Posterior end of alimentary canal.
This so-called third, upper or posterior conch is not a true conch, nor is that of the vestibulum; only the middle one forms a scroll, and this corresponds to the only one of reptiles and the lower of the mammals.
In relation to their parasitic habit one or two suckers are always developed, the one at the anterior and the other at the posterior end of the body.
Similarly during the growth of the bird the posterior end of the ilium connects itself with the transverse processes of vertebrae which were originally free, thus transforming them from caudals into secondary post-sacrals.