2. =V. mammaria interna= (_g_).--The internal mammary veins follow the corresponding arteries. The two veins unite to form a common trunk which, after receiving a branch from the cranial part of the sternum, enters the vena cava opposite the third rib. 3. =Vv. anonymæ= (Fig. 129, _m_; Fig. 115, _p_).--The innominate veins unite opposite the first intercostal space to form the vena cava superior. Each extends from the cranial end of the vena cava superior craniolaterad to a point a short distance craniad of the first rib and is there formed by the union of the =external jugular= (Fig. 129, _k_) and =subclavian= (_j_) veins. The innominate vein has the following branches: A and B. =Vv. vertebralis= and =costocervicalis= (_i_).--The vertebral and costocervical veins unite to form a single trunk which enters the innominate about opposite the first rib. These two veins follow the corresponding arteries. (Sometimes the vertebral and costocervical veins enter the innominate separately, and in other cases one or more of the components of the costocervical veins (e.g., the transversa colli) may enter the axillary vein. In other cases the entire common trunk of the vertebralis and costocervicalis may enter the superior vena cava directly.) C. =V. subclavia.=--The subclavian vein enters the innominate at about the level of the first rib. Outside of the thorax it is called the axillary vein (_j_); this comes from the arm. [Illustration: FIG. 130. SUPERFICIAL ARTERIES, VEINS, AND NERVES ON THE EXTENSOR SIDE OF THE ARM AND DORSUM OF THE HAND. _a_, V. cephalica; _b_, V. mediana cubiti; _c_, V. cephalica antibrachii; _d_, A. collateralis radialis superior; _e_, Aa. and Vv. digitales dorsales; _f_, A. radialis; _g_, superficial radial nerve; _h_, N. musculocutaneus; _i_, N. cutaneus medialis.] =Veins of the Arm.=--The blood is returned from the arm by two systems of veins,--a deep and a superficial system. The deep system is composed of veins which correspond to the branches of the axillary artery, follow in general the same course, and receive the same names (Fig. 122). They unite to form the axillary vein. The brachial vein does not pass with the brachial artery through the supracondyloid foramen. The superficial system comprises the vena cephalica and its branches.