504 THE ARTERIES OF THE LOWER LIMB. 



than usual or absent, the deficiency being- supplied by the tarsal artery, which famishes one 

 or more of the outer dorsal interosseous arteries (fig. 396). Occasionally there are two 

 metatarsal arteries. 



The dorsal interosseus arteries are sometimes derived mainly or solely from the plantar 

 arch, by means of the posterior perforating branches. 



SURGICAL ANATOMY OF THE ARTERIES OP THE LEG. 



The posterior tibial artery may be tied at any spot in the lower two-thirds of the leg. To 

 reach the artery in the middle third, an incision from three to four inches in length is made 

 through the skin and fascia, parallel to, and about half an inch behind, the internal border of 

 the tibia. The inner head of the gastrocnemius being drawn backwards, and the internal saphe- 

 nous vein (if exposed) forwards, the fleshy fibres of the soleus are cut through until the deep 

 aponeurosis of the latter muscle is reached. This is then divided for the whole length of the 

 wound, and the deep layer of fascia, which is here thin, is exposed. On laying this open the 

 artery is at once seen, being placed between the companion veins, and having the nerve to its 

 outer side. 



In the lower third of the leg, the artery is readily tied by means of an incision two inches 

 long, placed midway between the inner border of the tibia and the edge of the tendo Achillis, 

 and carried through the integument and the two layers of fascia. 



The peroneal artery might, if necessary, be secured in the middle third of the leg. An 

 incision, from three to four inches long, is made through the skin and fascia immediately 

 over the outer border of the fibula, and the soleus drawn backwards. The fibres of the flexor 

 longus hallucis are then to be raised from the posterior surface of the fibula, until the mem- 

 branous wall of the canal containing the vessel is exposed, and on laying this open the artery 

 will be found resting against the bone. 



In order to apply a ligature to the anterior tibial artery, an incision is made along the 

 front of the leg in the line of the vessel (see p. 501) for a distance of about three inches. In 

 the upper part a longer incision is necessary than in the lower, in consequence of the greater 

 depth of the artery, and a short transverse cut on each side through the dense fascia will 

 facilitate the subsequent steps of the operation. The areolar interval between the tibialis 

 anticus and the extensor longus digitorum is then opened up, and the muscles drawn well to 

 the sides ; in the lower part of the leg the extensor proprius hallucis must also be drawn 

 outwards. The artery is then found lying upon the interosseous membrane, or upon the bone, 

 according to the level at which it is exposed. The nerve is either superficial to, or on the 

 outer side of the vessels. In the lower third of the leg, the outer border of the tendon of the 

 tibialis anticus muscle is the best guide to the artery. 



The dorsal artery of the foot is tied by means of an incision an inch and a half in length, 

 placed midway between the tendons of the extensor proprius hallucis and extensor longus 

 digitorum muscles, and terminating below at the posterior end of the first intermetatarsal 

 space. On dividing the fascia, the artery is found passing beneath the innermost slip of the 

 extensor brevis digitorum, and having the companion nerve generally to its outer side. The 

 aponeurotic layer binding the vessels against the bone must also be cut through to bring them 

 fully into view. 



MORPHOLOGY OP THE ARTERIAL SYSTEM. 



The first portions of the great arteries, viz., the pulmonary trunk and the ascending aorta, 

 are to be regarded, so far as their development is concerned, as portions of the heart, being 

 formed from the foetal aortic bulb. The latter gives origin on each side to a series of 

 vascular arches, five, or it may be six, in number, which pass backwards in the wall' of the 

 foregut to join a longitudinal vessel the primitive dorsal aorta. The relation of these 

 arterial arches to the somatic and splanchnic arteries subsequently to be referred to is uncer- 

 tain. The changes which the arches undergo in the course of farther development are fully 

 explained in the section ''Embryology" in Vol. I, and are indicated also in fig. \ 333, on 

 p. 385 of this volume. They may be shortly stated as follows : From the lowest arches are 

 formed the pulmonary arteries, and on the left side .also the ductus arteriosus. The fourth 

 arch, with the common stem of this and the arches above, gives rise on the right side to the 

 innominate artery and the beginning of the subclavian, and on the left side to the arch of 

 the aorta. The elongated common stem of the upper three arches becomes the common carotid 

 artery, the third arch forms the internal carotid artery, and the common stem of the first 

 two arches furnishes the external carotid. 



Of the branches of the external carotid artery, the superior thyroid is the artery of the 

 median thyroid diverticulum, and therefore descends to the central part of the gland (the 

 inferior thyroid artery from the subclavian being the vessel of the lateral thyroid diverti- 

 culum, and passing to the outer and lower pirt of the gland) ; the lingual passes into the 



