THE VASCULAR SYSTEM 225 



tina from the floor of the mouth, one from the mandibular region, 

 and the other from the tissues on the dorsal side of the cerato-hyal, 

 but this would appear to be merely a variety of the type where both 

 regions drain into one vessel. 



Close to the point where the above vessel is received a small F. 

 pterygoidea (v.pt.) also enters. It arises in the posterior region of 

 the upper jaw and passes backwards along the ventral side of the 

 pterygoid. 



B. The external jugular may be regarded as comprising three main 

 venous factors: 



(I) The F. facialis communis (v.f.c), Vena jugularis externa 

 (Driiner), or Vena jugularis interna.'' (Bethge). This vessel collects 

 from three main regions, the orbit, the superficial intermandibular 

 region, and the thymus. It arises in the orbit. 



The superior 2.nd inferior palpebral veins (v.palp.s. and v.palp.i.) 

 collect blood from the upper and lower eyelids respectively. These 

 vessels unite at the posterior angle of the orbit where they are joined 

 by several small factors from the glandular tissue of that region to 

 form the superior facial vein. 



(i) The F. facialis superior (v.f.s.) passes backwards superficially to 

 the level of the thymus gland. It is closely applied to the skin, from 

 which it receives numerous branches, particularly from the large 

 paratoid gland of that region. In the region of the thymus it joins 

 its ventral counterpart — the inferior facial vein. 



(ii) The F. facialis inferior (v.f.i.) appears to arise at the tip of the 

 lower jaw from the genio-glossus muscle, and from an anastomosis 

 with the corresponding vessel of the opposite side, as the internal 

 mandibular vein. The F. mandihularis interna (v.m.i.) passes through 

 the loose connective tissue on the ventral side of the mandible. 

 Numerous factors are received from the intermandibularis muscle 

 and from the skin of the intermandibular region. At the posterior 

 border of the muscle an anastomosis is received from the V. mandihu- 

 laris profunda — a factor of the Internal Jugular — and from now on 

 the vessel is spoken of as the inferior facial vQ\n (v.f.i.). Continuing 

 along the ventral surface of the mandible it passes dorsal to the M. 

 interhyoideus and ventral to the M. interhyoideus posterior, receiv- 

 ing factors from both muscles. At the posterior angle of the lower 

 jaw it turns abruptly dorsalwards to join the superior facial vein at 

 the anterior border of the thymus as above described. 



Numerous factors from the thymus gland enter the combined 

 superior and inferior facial veins to form the common facial vein, 

 which then proceeds ventro-mesially to enter the ductus Cuvieri as 



