The pseuilobranchial circulation iu Amia calva. J|(j 



also had been partly covered by the growing lateral edge of the boue. 

 Slightly farther forward all three structures pass internal to, that is 

 dorsal to, a line of tissue that represents the as yet unossified lateral 

 wing of the parasphenoid, this wing thus lying, at this age, anterior 

 to the palatine foramen instead of covering it externally as in the 

 adult. On one side of the head a part of this lateral tissue had 

 become ossified, the little piece of bone so formed thus representing 

 a separate centre of ossification of the parasphenoid. 



Beyond the anterior edge of the wing of the parasphenoid the 

 internal carotid, accompanied by the two nerves, lies in an open, 

 angular space between the lateral edge of the parasphenoid and the 

 ventral surface of the chondrocranium, the latter surface being here 

 presented ventro-laterally. When the three structures reach the hind 

 edge of the large notch already described iu this part of the chondro- 

 cranium , the artery sends a small branch forward ventral to the 

 cartilage and itself passes upward and forward through the notch, 

 and reaches the dorsal surface of its anterior edge. The two nerves 

 accompany the small branch of the artery in its forward course 

 ventral to the cartilage, the two nerves soon anastomosing to form a 

 single nerve. The main artery is accompanied through the notch, as 

 already stated, by the efferent pseudobranchial artery, the two arteries 

 being here connected by an important communicating branch which 

 runs laterally, or laterally and forward, from one to the other. 



Continuing forward and mesially a short distance, the internal 

 carotid then turns directly forward and upward along the lateral sur- 

 face of the brain, and separates into three principal parts. The most 

 posterior of these three parts first runs upward along the lateral sur- 

 face of the bfain, and then backward and mesially, accompanying the 

 nervus oculomotorius. It lies immediately ventral to that nerve, and 

 connects, across the middle line of the head, with its fellow of the 

 opposite side. Its definite relations to the différent portions of the 

 brain were not investigated, but it must here lie in the dorsal part 

 of the space between the lobi inferiores and the anterior end of the 

 medulla oblongata. 



The second part of the artery joins the nervus opticus and enters 

 the eye-ball with it. 



The third part of the artery separates into two branches one of 

 which runs forward and outward, and could be traced to the edge of 

 the cartilaginous sclerotic near the insertion of the obliquus inferior 

 muscle. The other branch separates into two parts one of which goes 



