90 DEVELOPMENT OF PRIMITIVE BLOOD-VESSELS. 



difficult subject. He described the head-vein, in an embryo guinea-pig 2.5 mm. 

 long, as a vessel running from the region of the optic cup, close to the neural tube 

 (primitive vessel of the hind-brain), to the level of the first vertebra, where it 

 turned lateralward and lay lateral to the aorta (anterior cardinal vein), ending in 

 the duct of Cuvier. This vein (the primitive vessel of the hindbrain), was mesial 

 to the cranial nerves, and Salzer called it the anterior cardinal vein. It was a 

 transitory vein, for by the time the embryo was 2.8 mm. long he found a second 

 vein, lateral to the nerves, from the region of the acoustico-facial complex for- 

 ward. This second vein he called the vena capitis lateralis, and concluded that, 

 not only in the guinea-pig but in vertebrates in general, the anterior cardinal 

 vein (deep channel of the hindbrain) is the first vein to develop in the head, and 

 that it is replaced by a vena capitis lateralis, which as the neck develops is con- 

 tinued into the neck as the internal jugular vein. This description of the veins 

 of the early embryo by Salzer is nearly correct, and was a great step in advance, 

 though more complete studies give a different interpretation and naming of the 

 veins. 



The next step was made in 1907, by Dr. Mall, who studied the cerebral 

 sinuses in the human embryo and, on the basis of this work of Salzer, demon- 

 strated that the first drainage canal for the head (primary head-vein including 

 the anterior cardinal) gives rise to the cerebral sinuses and the internal jugular 

 vein. This drainage canal (the vena capitis prima) he called the anterior cardinal 

 vein, using the term in its generally accepted sense as applying to the entire head- 

 vein and neck- vein of the embryo. 



In the same year Grosser made it clear that the first vascular channel for 

 the head (deep vessel of the hindbrain and the anterior cardinal) can be analyzed 

 into two parts: a cephalic part which lies close to the neural tube, and a caudal 

 part which has an entirely different position namely, ventral to the myotomes 

 and lateral to the aorta, in the same position as the posterior cardinal vein. He 

 limited the term "anterior cardinal vein" to this caudal portion, and analyzed 

 the cerebral portion into a primary vessel (the vena capitis medialis) and a sec- 

 ondary vein (the vena capitis lateralis). 



At this point Evans gave his beautiful injections of early blood-vessels, 

 published in 1909. He showed the form of the primitive vascular plexus of the 

 brain and also how this plexus covered the surface of the forebrain, encircling 

 the large optic vesicle with a chain of capillaries and spreading over the surface 

 of the thalamus and midbrain. He described how this extensive plexus became 

 a single slender channel along the wall of the hindbrain, leading down to the 

 transverse vein and the duct of Cuvier; and also demonstrated the connections 

 of the plexus of the forebrain and the single vessel of the hindbrain with the aorta. 



Streeter has recently published a study dealing with the later stages of the 

 vena capitis prima. It was from the branches of this vein that Dr. Mall had 

 shown that the dural sinuses were derived. Streeter has worked out the develop- 

 ment of the dural sinuses more in detail and has shown that the only part of the 

 vena capitis prima to persist is the part mesial to the Gasserian ganglion which 



