ANGEIOLOGY. 95 
former pierces the interosseous ligament, and inosculates with the external 
malleolar; the latter spreads its branches on the outer side of the heel and 
of the foot. 
The internal plantar artery proceeds along the internal side of the sole, 
and inosculates with the adjacent vessels. The external plantar, much the 
larger, passes forward as far as the fifth metatarsal bone ; it then crosses the 
metatarsus, and joins the anterior tibial, to form the plantar arch. 
Pi. 185, fig. 15’, sartorius muscle, cut off; *, hole in the tendon of the 
adductor magnus; *, femoral artery; *, superficial epigastric; °, profunda 
artery ; *>*, perforating branches of the profunda; °, internal, **, external 
circumflex arteries; *’, superficial pudic; “, popliteal artery. Mig. 17’, 
anastomotica; *, anterior tibial; *, recurrent branch; *, external, °, internal 
malleolar ; °, tarsal vessels; ', metatarsal vessels; “an artery of the toes. 
Fig. 16, plantar arteries: *, posterior tibial artery; *, internal, *, external 
plantar arteries; *, deep plantar arch; °, a branch to the back of the foot. 
*, a metatarsal artery ; ’, its division into two branches ; *, union of two such 
branches; °, division into the arteries of the toes; “, union of two such 
divisions; “, vascular plexus at the tip of the toes. 
3. THE VEINS. 
The veins commence in the capillary system, and are therefore continu- 
ous with the arteries: in some parts they appear to arise out of a cellular 
or spongy intermediate structure, although this may be nothing more than a 
venous plexus. From the:origins the veins unite and form larger branches, 
which ultimately end in two great trunks. Both small and large veins are 
remarkable for their numerous anastomoses, and large veins are often seen 
to divide and unite again. 
‘Veins are composed of the same number of coats as arteries, but the 
middle lamina is much thinner, therefore they collapse when empty or when 
divided. The external or cellular coat is similar to that of arteries; the 
middle or fibrous coat wants the external elastic lamina, but possesses the 
two other layers of contractile fibres, the external circular and the internal 
longitudinal ; the third, or innermost, or serous coat is stronger, but similar 
to that of the arteries, being, indeed, continuous with it through the capilla- 
ries on the one hand, and the cavities of the heart on the other. The most 
striking peculiarity in this tissue is seen in the presence of numerous semi- 
lunar folds or valves; each of these is composed of a duplicature of the 
membrane, inclosing some fibrous cord. Their concave floating end is 
towards the heart, and therefore the blood in its: course towards this organ 
meets no resistance from the valves, while they present serious obstacles ‘to 
its reflux. ‘These valves are sometimes in pairs, sometimes single; they are 
most numerous in the extremities and in the deep veins, and are generally 
found at points of confluence; they are absent in very small veins, and in 
the large trunks, as the cave, iliacs, internal jugular, and innominata; also 
in the cerebral veins, and in the whole of the portal system. 
ICONOGRAPHIC ENCYCLOPADIA.—VOL, II. 51 801 
