18 THE DEVELOPMENTAL ALTERATIONS IN THE VASCULAR SYSTEM 



primary head-vein that was described by different writers as the anterior cardinal 

 vein until Grosser (1907) showed that only the caudal portion of it— the part that 

 is found in the region of the somites and later forms the internal jugular vein — 

 could be properly spoken of as the anterior cardinal. Salzer (1895) designated 

 the portion in the presegmental region 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 

 alwaj's found median to the nerve and hence is always vena capitis mediaUs. Caudal 

 to the trigeminal nerve, Salzer describes it as at first coursing medial to the facial, 

 glossopharyngeal, and vagus nerves, and subsequently, by a process of "island 

 formation," 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, and were used in the 

 recent paper by Shindo (1915). We now know, however, from the work of Sabin 

 (1917a) that what Salzer called the vena capitis medialis is the primordial channel 

 of the hindbrain, whose purpose is primarily the proliferation of endothelium, and 

 hence is not to be regarded as a pure drainage-channel. The primary head-vein 

 is the first true drainage-channel in this region. Its composite origin has already 

 been pointed out. It has been shown 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 cavern- 

 ous sinus, the otic or more 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 join it mainly along its 

 dorsal margin, though there are also ventral tributaries which are especially large 

 and numerous in the neighborhood of the optic stalk and the trigeminal ganglion, 

 as seen in figures 24 and 25. A large plexiform sheet Ues median to the maxillary 

 trunk of the trigeminal nerve, draining the structm-es of the maxillary arch. It is 

 continuous with the plexus that envelops and penetrates into the substance of the 

 trigemmal ganglion. It is a modification of this plexus that forms the infraorbital 

 vein and the venous plexus in the region of the pterygoid fossa. The ophthalmic 

 vein corresponds to the ventral tributaries just in front of this and median to the 

 first division of the trigeminal nerve. This is contrary to the view of Markowski 

 (1911, p. 600), who thought that it was the more caudal and larger of these tribu- 

 taries, the one draining the maxillary process, that becomes the ophthalmic vein; 

 whereas the more anterior tributaries, arising from the orbital fossa, he described 

 as undergoing retrogression and disappearing. That it does not disappear, but 

 forms the main portion of the ophthahnic vein, we shall be able to see in older stages. 



The tributaries drainmg dorsally mto the primary head-vein are arranged 

 in three plexiform groups, as was pointed out by Mall (1905), the first group empty- 

 ing into the main channel in front of the semilunar ganghon, the second group 

 between the semilunar and the acustico-facial gangUa, and the third group caudal to 

 the otic capsule. .These were designated respectively the anterior, middle, and pos- 



