1101 



VENOUS SYSTEM. 



to a lobe of the lungs. There are consequently 

 three venous trunks for the right lung, and 

 two for the left. On the right side the branch 

 from the middle lobe unites with that from 

 the superior; and hence two pulmonary veins, 

 one superior to the other, are usually found in 

 the root of each lung, where on both sides 

 they are placed below but on a plane anterior 

 to the pulmonary artery and bronchial tube. 

 In the substance of the lungs the relative po- 

 sition of these parts is different, for there the 

 branches of the veins are behind, whilst those 

 of the artery are in front, the bronchus being 

 interposed between both. 



The four pulmonary veins then perforate 

 the pericardium, and alter a short course enter 

 the most posterior part of the left auricle, 

 those of the left side opening very close to- 

 gether, and not unfrequently by a common 

 orifice. 



Within the pericardium these veins are in- 

 vested by its serous membrane, but on their 

 anterior surfaces only. In passing to their 

 destination, the right pulmonary veins lie 

 behind the right auricle of the heart. 



II. THE SYSTEMIC VEINS. 

 The veins of this system will be described 

 in the following order. 



A. The veins which form the vena cava 

 superior, and which are derived from the head, 

 face, neck, thorax, and upper extremities. 



Amonst these the veins of the parieties of 

 the thorax (azygos veins), and those of the 

 spinal column (rachidiau veins), are remarkable 

 as serving to connect the branches of the 

 superior with those of the inferior vena cava. 



B. The veins which form the vena cava 

 inferior, and which convey the blood from the 

 lower extremities and from the pelvic and 

 abdominal cavities. The portal veins are an 

 adjunct to this system. 



c. The proper veins of the heart (cardiac 

 veins), which arise in the substance of that 

 organ, and open by a separate trunk into the 

 right auricle. 



A. THE VEINS WHICH FORM THE VENA 

 CAVA SUPERIOR. 



These are constituted by the veins, 1. Of 

 the head and face ; 2. Of the neck; 3. Of the 

 upper extremities ; 4 . Of the thorax. 



I . Veins of the head and face. * The super- 

 ficial veins of the head and face unite to form 

 three principal trunks, which are placed on the 

 anterior, lateral, and posterior aspects of the 

 cranium ; anteriorh/ is seen the 



Facial vein. This vein originates in the 



* The veins of the head may be divided into two 

 sets, those which ramify on its exterior and those 

 which occupy its interior ; the former will alone be 

 noticed in this place. The latter, which are repre- 

 sented by the cerebral veins and sinuses of the dura 

 muter, are described in Article NERVOUS CENTRES 

 (Dr. Todd), Vol. III. C31. Intermediate to these 

 two systems are the veins of the bones of the head 

 (the diploic veins), which, by their inosculations 

 with both, maintain a free communication between 

 the superficial and deeper seated veins. For a de- 

 scription of the diploic vein.", see Art. BONE, 

 Vol. I. p. 430. 



frontal region from numerous interlacing 

 branches, which usually give rise to one 

 large vein on each side (frontal vein), which is 

 joined by branches from the upper lid (palpe- 

 bral) and root of the nose, and by the supra- 

 orbital vein ; sometimes there is but one frontal 

 vein placed in the mesial line, and dividing 

 into two branches, which descend one on 

 either side of the nose. The frontal vein 

 continues its course in the sulcus along the 

 inner margin of the orbit under the name of 

 angular vein, accompanying the artery of the 

 same name, and receives numerous branches 

 from the orbit, by which a close connexion 

 is maintained between the circulation on the 

 exterior of the cranium and that of the cere- 

 brum itself. At the lower margin of the orbit 

 the angular becomes the proper facial vein, 

 which passes downwards and outwards in an 

 almost direct course to the anterior edge of 

 the insertion of the masseter muscle. 



The facial vein consequently has a much 

 shorter extent than its corresponding artery, 

 to the outer side of which it is invariably 

 placed ; it passes beneath the zygomatic mus- 

 cles, and lies on Steno's duct, just where the 

 latter is about to penetrate between the fibres 

 of the buccinator muscle. 



The facial vein receives the following branches. 

 Veins from the alae nasi, the coronary, buccal, 

 infra-orbital, and masseteric veins ; and also 

 several large communicating veins (deep facial 

 or alveolar) from a venous plexus which is 

 lodged in the pterygoid space. 



Having passed below the ramus of the jaw, 

 the facial vein enters the digastric space, which 

 it traverses from above downwards and back- 

 wards, and lies beneath the platysma myoides 

 and on the submaxillary gland (which con- 

 sequently is interposed between the facial vein 

 and artery) ; this vein next passes across the 

 external carotid artery to terminate in the 

 internal jugular vein, having been previously 

 joined by a large branch of communication 

 from the temporo-maxillary vein. In its 

 course through the digastric space the facial 

 vein receives (a), the ranine vein, which comes 

 from the inferior surface of the tongue, passes 

 backwards by the side of the fraenum, and 

 accompanies the hypoglossal nerve, between 

 the m}lo-hyoid and hyo-glossus muscles; 

 (b), the satellite vein of the gustatory nerve, 

 which is derived from a plexus of superficial 

 veins on the dorsum of the tongue, and com- 

 municates freely with the preceding (Cruveil- 

 hier); (c), the subiiiental vein, which arises in 

 the sublingual gland ; and (d) several palatine 

 veins which are derived from a venous plexus 

 encircling the tonsil. 



In many instances the facial vein unites 

 with the proper lingual veins, and thus forms 

 a common trunk, which throws itself into the 

 internal jugular ; into this common trunk the 

 superior thyroid, pharyngeal, and temporo- 

 maxillary veins, will in such a case be fre- 

 quently found to open. 



On the lateral region of the head are placed 

 the trunks of the temporal and internal max~ 

 ill ary , veins. 



