POSTERIOR TIBIAL VEINS. 613 



tibia, and passes outwards beneath the flexor pollicis, to unite in an arch 

 with a corresponding offset of the peroneal artery. 



d. Articular branches arise from the artery opposite the ankle-joint, 

 and enter the articulation. 



e. Cutaneous offsets appear through the fascia in the lower half of the 

 leg ; the largest of these pierces the annular ligament, and accompanies 

 the cutaneous plantar nerve to the sole of the foot. 



Peculiarities. If the posterior tibial artery is smaller than usual, or absent, its de- 

 ficiencies in the foot will be supplied by a large communicating branch from the 

 peroneal artery, which is directed inwards at the lower end of the tibia, and either 

 joins the small tibial vessel, or runs alone to the sole of the foot. 



The PEROXEAL ARTERY (fig. 209, a) is often as large as the posterior 

 tibial, and arises from that vessel about one inch and a half from the begin- 

 ning. It takes the fibula as its guide, and lying close to that bone in the 

 fibres of the fiexor pollicis, reaches the lower part of the interosseous mem- 

 brane. At this spot it sends forwards a branch to the front of the leg 

 (anterior peroneal) ; and it is directed onwards over the articulation be- 

 tween the tibia and fibula (A) to the outer side of the heel, where it termi- 

 nates in branches, which anastomose with offsets of the posterior tibial, and 

 with the tarsal and external plantar arteries. 



Two companion veins surround the artery ; and the nerve to the flexor 

 pollicis lies on it generally. 



-Branches. Besides the anterior peroneal, it furnishes muscular, nutri- 

 tious, and communicating offsets. 



a. Muscular branches are distributed to the soleus, tibialis posticus, and 

 flexor pollicis ; and some turn round the fibula to the peronei muscles, 

 lying in grooves in the bone. 



b. The nutritious artery is smaller than that to the tibia, and is trans- 

 mitted through the tibialis posticus to the aperture about the middle of 

 the fibula, 



c. The anterior peroneal branch passes forwards through an opening 

 in the lower part of the interosseous membrane, and is continued to the 

 dorsum and outer part of the foot ; on the front of the leg and foot it anas- 

 tomoses with the external malleolar and tarsal branches of the anterior 

 tibial artery. 



d. A communicating offset near the ankle joins in an arch with a simi- 

 lar branch of the posterior tibial. Sometimes there is a second arch be- 

 tween the same vessels. 



Peculiarities. The anterior branch of the peroneal may take the place of the 

 anterior tibial artery on the dorsum of the foot. 



A compensating principle may be observed amongst the arteries of the foot as in 

 those of the hand, by which the deficiency in one is supplied by an enlarged off- 

 set of another. 



The POSTERIOR TIBIAL VEINS begin on the inner side of the foot by the 

 union of the plantar: they ascend one on each side of the artery, and unite 

 with the anterior tibial at the lower border of the popliteus to form the 

 large popliteal vein. They receive the peroneal veins, and branches cor- 

 responding with the offsets of the artery ; branches connect them with the 

 saphenous veins. 



The POSTERIOR TIBIAL NERVE (fig. 201), 3 ) a continuation of the inter- 

 nal popliteal, reaches, like the artery, from the lower border of the popli- 

 teus muscles to the interval between the os calcis and the inner malleolus. 



