VENOUS SINUSES OF THE DURA MATER 147 



time the otic vesicle has differentiated far enough to make it 

 possible to recognize the situation of the endolymphatic append- 

 age. Before this time certain important phases in the develop- 

 ment of the blood vessels of the head have already occurred. 

 These will now be briefly reviewed as an introduction to the 

 subsequent conditions. 



PRIMARY VASCULARIZATION OF HEAD 



The most complete account we have of the vascularization of 

 the brain and its earliest drainage is based on the chick and the 

 pig. For descriptions of these we are largely indebted to Evans 

 ('09, '12). According to this author, the first blood vessels to 

 the brain take the form of a capillary plexus that sprouts out 

 from the aortic arch. These sprouts form a vascular web that 

 closely invests the neural tube, beginning in the region just 

 caudal to the optic stalk and spreading from there up over the 

 adjacent fore- and mid-brains. By the coalescence of other cap- 

 illary sprouts from the dorsal aorta a continuous channel is estab- 

 lished along the side of the hind-brain that drains these capil- 

 laries of the head caudalward toward the venous end of the heart. 



A study of the cardinal veins in the chick has recently been 

 made by Professor Sabin ('14, '15) in this laboratory, and she 

 has kindly demonstrated her specimens to me. From these speci- 

 mens the development of the drainage of the primary brain 

 plexus can be plainly made out. In the head region, proper, 

 capillary sprouts from the dorsal aorta fuse into a continuous 

 channel that drains the brain plexus caudalward to the vagus 

 region. At this point it joins a small capillary plexus in which 

 the anterior cardinal vein is to form. This latter plexus is one 

 that develops between the aorta and the vitelline vein. It has 

 been demonstrated by Professor Sabin that it differs from the head 

 plexus in two essential particulars: (1) The sprouts from the aorta 

 from which it is formed bear a definite relation to the cervical 

 myotomes; (2) These sprouts also bear a definite relation to the 

 nephrotomes and thus identify themselves as belonging to the 

 cardinal system. Shortly after the time that this plexus is joined 



