230 THE VASCULAR SYSTEM. 



(6) A larger vessel, the Ramus maxillaris inferior (Fig. 148 m"), 

 which arises from the Ramus maxillaris superior under cover of the 

 tympanic membrane, and accompanies the Ramus mandibularis of 

 the trigeminal nerve through the M. masseter, or between this 

 muscle and the M. temporalis to the mandible, and then courses 

 forwards to the chin. A large cutaneous branch is given off half- 

 way along the floor of the mouth. The artery gives off many 

 small twigs to supply the neighbouring structures.] 



3. The pulmo-cutaneous arch (Dnctus pulmo-cutaneus], Figs. 

 132, 143, and 145 ///) is the hindmost (fifth embryonic) of the 

 three persistent arches; it passes upwards and forwards on the 

 oesophagus, and at the level of the carotid gland divides into two 

 branches, the pulmonary artery and the cutaneous artery. 



a. The pulmonary artery (Arteria pulmonalis} runs backwards to 

 the root of the lung, along the outer surface of which it is continued 

 in a sinuous course. It supplies the lung. 



b. The cutaneous artery (Arteria cutanea magna\ (Fig. 149 c.m.] 

 [passes along the deeper surface of the M, pelrohyoidem ///until near 

 the prootic bone ; in this course it travels forwards, outwards, and 

 upwards, crosses the outer border of the muscles, and appears between 

 the M. levator anguli scapulae and the M. sternocleidomastoideus. At 

 this point the artery curves sharply round to reach the angle of the 

 jaw, the hinder border of the M. depressor maxillae inferioris. The 

 curve so formed and the descending limb are covered by the M. 

 depressor maxillae inferioris. The artery then passes backwards to 

 form a rich anastomosis in the skin almost as far as the posterior 

 end of the trunk. It supplies the following branches : 



(1) The Ramus dorsalis (Virchow) arises immediately in front of 

 the curve of the main artery; it ascends behind the M. temporalis, 

 and passes along the anterior border of the M. depressor maxillae to 

 the skin, where it curves backwards. It supplies small twigs 

 forwards as far as the eyelids. 



(2) The Ramus auricularis (Virchow) also arises in front of the 

 curve in the cutaneous artery; sometimes it arises from the Ramus 

 dorsalis. The artery winds around the M. petroliyoideus III near its 

 insertion, and so reaches the posterior wall of the tympanic cavity, 

 where it anastomoses with the R. auricularis of the Ramus maxillaris 



(3) The Arteria pharyngo- maxillaris (Fig. 148 p.m.] is a small 

 branch running forwards and outwards to supply the mucous mem- 

 brane of the larynx, Eustachian tubes, gums, the lower jaw, and 



