DEVELOPMENT OF PRIMITIVE BLOOD-VESSELS. 89 



As far as the relations of the vena capitis prima to the vessels of the adult 

 are concerned, it has been shown by Mall and Streeter that only a very small 

 portion of the primary head-vein persists within the skull cavity namely, the' 

 segment just mesial to the Gasserian ganglion which becomes the cavernous 

 sinus. The neural branches of the primary head-vein ultimately give rise to the 

 other dural sinuses. 



In regard to the relations of the anterior cardinal vein of the embryo to the 

 internal jugular vein, it is interesting to note, in plate 6, that the entire anterior 

 cardinal vein is opposite occipital myotomes; that is, it is entirely within the head. 

 The caudal part of the anterior cardinal vein will become a vein of the neck when 

 the duct of Cuvier shifts into the zone of the cervical myotomes. The cephalic 

 end of the anterior cardinal vein of the embryo is opposite the upper zone of the 

 medulla. The cardinal system of veins in general covers the entire zone of the 

 myotomes, which includes a part of the head as well as the entire body of the 

 embryo. 



In closing this account of the origin of the primary head-vein, it is important 

 to emphasize again the relation of the new vessel, the middle portion of the vena 

 capitis prima, to the various structures related to the hindbrain that is, to the 

 otic capsule and to the ganglia of the hindbrain. The middle portion of the 

 head-vein develops after these structures are formed and must conform to their 

 position. It grows in as straight a line as possible, and passes mesial to the 

 placode of the trigeminus, lateral to the acoustic complex, to the otic capsule, 

 and to the ganglion of the glosso-pharyngeus. It is entirely a new vessel, and 

 has no remnants whatever of the preliminary vascular channel of the hindbrain 

 which arises and runs along the neural tube. As is seen in plate 6, there are two 

 entirely distinct vessels in the head of a chick of the early part of the fourth day 

 the so-called vena capitis mesialis, a neural vessel, and the so-called vena capitis 

 lateralis, a true head-vein. 



After following this account of the origin of the primary head-vein of the 

 chick, it will be of value to consider the long series of previous studies upon which 

 it has .been based. The observations which seem to me to lead to a clear under- 

 standing of this subject are those of Salzer, Mall, Grosser, Evans, Williams, and 

 Streeter. The view first held in regard to the development of the veins of the 

 head was that the external jugular vein was the primary vein of this region. This 

 view, which was incorrect, was based on the work of Rathke. In 1887 Kastschenko 

 described a remarkable relationship between the jugular vein and the cranial 

 nerves in the chick. He stated that up to the end of the third day the cranial 

 nerves were lateral to the jugular vein (primitive vessel of the hindbrain), and 

 noted that this vein was not in the form of a plexus. At the end of the third day 

 the facial and glosso-pharyngeal nerves became mesial to the vein, and on the 

 sixth day the vagus became mesial. He thought that the nerves cut through the 

 veins, as it were, without the latter losing their continuity. 



In 1895 Ralzer published an article on the development of the veins of the 

 head in the guinea-pig, which forms the basis of the correct interpretation of this 



