I answer that, The movement of the appetitive power follows an act of the apprehensive power.  Now the apprehensive power apprehends a thing in two ways.  First, by way of an incomplex object, as when we understand what a man is; secondly, by way of a complex object, as when we understand that whiteness is in a man.  Consequently in each of these ways the appetitive power can tend to both good and evil:  by way of a simple and incomplex object, when the appetite simply follows and adheres to good, or recoils from evil:  and such movements are desire, hope, pleasure, sorrow, and so forth:  by way of a complex object, as when the appetite is concerned with some good or evil being in, or being done to, another, either seeking this or recoiling from it.  This is evident in the case of love and hatred:  for we love someone, in so far as we wish some good to be in him; and we hate someone, in so far as we wish some evil to be in him.  It is the same with anger; for when a man is angry, he wishes to be avenged on someone.  Hence the movement of anger has a twofold tendency:  viz. to vengeance itself, which it desires and hopes for as being a good, wherefore it takes pleasure in it; and to the person on whom it seeks vengeance, as to something contrary and hurtful, which bears the character of evil.

We must, however, observe a twofold difference in this respect, between anger on the one side, and hatred and love on the other.  The first difference is that anger always regards two objects:  whereas love and hatred sometimes regard but one object, as when a man is said to love wine or something of the kind, or to hate it.  The second difference is, that both the objects of love are good:  since the lover wishes good to someone, as to something agreeable to himself:  while both the objects of hatred bear the character of evil:  for the man who hates, wishes evil to someone, as to something disagreeable to him.  Whereas anger regards one object under the aspect of evil, viz. the noxious person, on whom it seeks to be avenged.  Consequently it is a passion somewhat made up of contrary passions.

This suffices for the Replies to the Objections.
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THIRD ARTICLE [I-II, Q. 46, Art. 3]

Whether Anger Is in the Concupiscible Faculty?

Objection 1:  It would seem that anger is in the concupiscible faculty.  For Cicero says (De Quaest.  Tusc. iv, 9) that anger is a kind of “desire.”  But desire is in the concupiscible faculty.  Therefore anger is too.

Obj. 2:  Further, Augustine says in his Rule, that “anger grows into hatred”:  and Cicero says (De Quaest.  Tusc. iv, 9) that “hatred is inveterate anger.”  But hatred, like love, is a concupiscible passion.  Therefore anger is in the concupiscible faculty.

Obj. 3:  Further, Damascene (De Fide Orth. ii, 16) and Gregory of Nyssa [Nemesius, De Nat.  Hom. xxi.] say that “anger is made up of sorrow and desire.”  Both of these are in the concupiscible faculty.  Therefore anger is a concupiscible passion.