152 GEORGE L, STREETER 



and later forms the internal jugular vein — could be properly- 

 spoken of as the anterior cardinal. The portion in the pr seg- 

 mental region was designated by Salzer ('95) in the guinea-pig 

 as 'vena capitis medialis' and 'vena capitis lateralis/ depending 

 on whether it was found median or lateral to the cranial nerve 

 trunks. The more cephalic portion, in the trigeminal region, is 

 always found median to the nerve and hence is always vena 

 capitis medialis. Caudal to the trigeminal nerve Salzer de- 

 scribes it as at first coursing medial to the facial, glossopharyngeal 

 and vagus nerves, and subsequently, by a process of 'island for- 

 mation,' migrating lateral to these same nerves, that is, changing 

 from vena capitis medialis to vena capitis lateralis. These 

 terms were advocated on the basis of an homology with similar 

 veins in the lower vertebrates. The importance of vascular 

 homologies practically disappears on the acceptance of the Aeby- 

 Thoma conception of the adaptive capillary formation of blood 

 vessels, which has been so clearly established by the brilliant 

 chick injections of Evans ('09) and therefore in this paper the 

 terms vena capitis medialis and vena capitis lateralis will not be 

 used. It is felt that the term 'primary head vein,' covering 

 both of them, will be less confusing and will be entirely adequate 

 from the youngest stages up to embryos about 20 mm. long. 

 The composite origin of this vein, however, should not be for- 

 gotten. It has already been pointed out that it belongs in part 

 to the trunk (the anterior cardinal vein) and in part is intrinsic 

 to the head. As we shall presently see, it is the trunk portion, 

 or anterior cardinal, that forms the internal jugular vein, whereas 

 the intrinsic head portion in its more anterior segment becomes the 

 cavernous sinus, the posterior portion (the so-called vena capitis 

 lateralis) disappearing entirely and being replaced by a more 

 dorsally situated channel. 



The tributaries draining into the primary head vein are ar- 

 ranged in three plexiform groups (fig. 2), as was pointed out by 

 Mall ('05), the first group emptying into the main channel in 

 front of the semilunar ganglion, the second group between the 

 semilunar and the acustico-facial ganglia, and the third group 

 caudal to the otic capsule. These were designated respectively 



