DEVELOPMENT OF PRIMITIVE BLOOD-VESSELS. 93 



small intersegmental veins. Thus it may be said that two organs determine the 

 early blood-vessels, the neural tube, and the nephrotome. Soon a third set of 

 organs (the visceral clefts) develop and give rise to capillaries, which connect on 

 the one hand with the anterior veins of the brain and on the other with the 

 cardinal veins; and in this manner the head-vein of the embryo is completed. 



The method of nomenclature of the primitive vessels of the head is certainly 

 open to discussion. The primitive vessel of the hind-brain, of which I have shown 

 the origin, the relations, and the fate, is the vessel seen by Kastschenko in 1887 

 and more clearly by Salzer in 1895, and recognized by all who have since worked 

 on this subject as being the first long vein in the head region and as lying along the 

 wall of the hindbrain. Grosser gave it the name of "vena capitis medialis," a 

 name which has been universally accepted. 



It may be argued that it is a mistake to attempt to change a name of this 

 type which has been generally adopted; but on the other hand a name which would 

 emphasize the essential point in regard to this vessel namely, that it is a neural 

 vessel and that it develops into neural vessels rather than the accessory fact 

 that it serves temporarily as a vein for the head, would, I am convinced, clear up 

 much of the confusion in regard to the primitive veins of the head. It does serve 

 for two days in the chick as a vein for the forebrain and the midbrain, but at the 

 same time it is the entire capillary bed of the hindbrain and ceases to be a single 

 long channel as soon as the cerebral blood is shunted through another channel. 

 It then develops, as have the rest of the neural vessels, into an extensive capillary 

 plexus in the position of the pia mater. I therefore wish to avoid the use of the 

 term vein in connection with it and to reserve the term vein for the vena capitis 

 lateralis, for which I shall use the term vena capitis prima, because this is the first 

 vascular channel of the head which is purely a vein and because it is the first vessel 

 which drains the head and not the brain alone. I have therefore called the vena 

 capitis medialis the primitive vessel of the hindbrain. The term vessel is more 

 indefinite than the term vein, but for that very reason it applies better to a channel 

 which serves both as a vein and as a capillary at the same time, and ultimately 

 becomes a capillary plexus, out of which both arteries and veins will arise. I propose 

 to call the long vein of plate 6, extending from the region of the thalamus to the 

 duct of Cuvier, the primary head- vein. This primary head-vein develops in 

 three segments a cephalic segment which is the primitive cerebral vein, a middle 

 segment opposite the hindbrain, and a caudal segment which is the vena car- 

 dinalis anterior. At the stage of plate 6 this vein is entirely within the head, 

 because the duct of Cuvier is still opposite occipital myotomes. As soon as the 

 duct of Cuvier shifts into the neck region this vein will become the primary head 

 and neck vein. The terms vena capitis medialis and lateralis have the sanction 

 of usage; but it seems to me that the terms primitive vessel of the hindbrain 

 and primary head-vein better express the function of these vessels. 



