THE VASCULAR SYSTEM 221 



Veins entering the Heart direct. 



Veins of the Head (PI. XV and PI. XIX, fig. 70). 



A. F. jugularis interna (internal jugular vein) (v.j.i.). This 

 important vein may be said to be formed by the fusion of two 

 main factors. One of these lies latero-dorsal to the aortic arches and 

 returns the blood from the occipital region and the muscles of the 

 *neck', and may be called the V. jugularis lateralis (v.j.L). The other 

 lies ventro-mesial to the internal carotid and the dorsal part of the 

 systemic arch and drains the palate. This factor is the F. pharyngo- 

 palatina (v.ph-p.) (Druner). There are anastomoses between these 

 two vessels that make it difficult to decide exactly which factors 

 belong to each, and particularly is this so in the case of the V. petrosa 

 lateralis, as it discharges into both vessels. It has been included 

 among the factors of the V. pharyngo-palatina, as the contribution 

 to this vessel is larger, and it also anastomoses with some of its 

 palatine factors. 



Owing to the large amount of individual variation met with, par- 

 ticularly in the palatine region, it is very difficult to give a detailed 

 description of the factors of the veins of the head. Only the more 

 constant features have been noted therefore, together with some 

 indication of the types of variation to be expected. 



Factors of the F. jugularis lateralis. 



(a) RR. musculares from the MM. cucullaris and opercularis. 

 These enter the vein variously as it passes along the ventral edge of 

 the muscles. 



{jy) F. occipitalis (occipital vein). This vein arises just behind the 

 head, between the MM. inter-transversarius capitis superior and 

 inferior, by factors from these muscles and from the M. opercularis. 

 It also receives : 



(i) A small F.post-occipitalis from the cranial cavity, which passes 

 through a foramen in the first vertebra, as in the Frog. 



(ii) A F. cranialis post-otica (sinus jugularis. Rex) from the region 

 of the medulla. This factor emerges from the cranial cavity together 

 with the ninth and tenth cranial nerves. 



(iii) A R. muscularis from the M. cucullaris, passing dorsal to the 

 X+X ganglion. 



(iv) An anastomosing factor from the vertebral vein. 



The occipital vein joins the main vessel ventral to the IX+X 

 ganglion. 



(c) F. vertehralis (v.v.). The vertebral vein is one of the most 



