The pseudobranchial circulation in Araia oalva. 113 



anterior and lateral edges of this notch are formed by that part of 

 the strip of cartilage that lies slightly removed from the brain. The 

 I)osterior, or postero-raesial edge is formed by that part of the car- 

 tilage that lies closely against the brain. As the notch extends 

 postero-laterally into the strip, the posterior edge of the notch here 

 forms a small process directed forward. On this process the recti 

 muscles, with the exception of the rectus externus, have their insertions. 

 This edge of the notch, on each side of the head, thus represents, at 

 this age, a lateral part of the transverse, cartilaginous, basisphenoidal 

 bar of the adult, the two parts of the bar not being in any way 

 directly connected with each other across the under surface of the 

 brain. Slightly in front of the notch the lateral parts of the two 

 strips become united under the brain and form a continuous, trans- 

 verse, cartilaginous basis cranii. 



The eiferent pseudobranchial artery, running forward and mesially, 

 anterior to the pseudobrauchial cleft, passes along the external surface 

 of the lateral wing of the parasphenoid, and, in front of that wing, 

 runs dorsal to the ramus palatinus posterior facialis, as already de- 

 scribed, for older stages, in my earlier work. In front of the latter 

 nerve the artery reaches the notch, above described, that represents 

 its own foramen united with that of the internal carotid, and passes 

 upward and forward through it, lying slightly dorso- lateral to the 

 internal carotid and receiving from that artery a relatively large and 

 important communicating branch. Immediately anterior to this com- 

 municating branch the efi'erent pseudobranchial artery turns rather 

 sharply upward, forward and laterally, the communicating branch thus 

 being given olï at the summit of a sharp bend in the elïerent artery. 

 The latter artery then enters the hind end of the orbit, and there 

 has the course already described in the adult, in my earlier work, 

 but it lies relatively much farther from the nervus opticus than in 

 the adult, entering the eye-ball with the ciliaris brevis considerably 

 posterior to the point where the opticus enters it. 



Immediately posterior to the pseudobranch the posterior con- 

 tinuation of the efferent pseudobranchial artery turns sharply laterally, 

 and running slightly downward and backward passes outward in the 

 angle between the anterior edge of the hyomandibular cartilage and 

 the posterior edge of the pterygo-quadrate. There, in the specimen 

 cut in transverse sections, it turned downward along what seemed to 

 be the lateral surface of the pterygo-quadrate, this cartilage and the 

 hyomandibular here being so continuous that it was impossible to 



Zool. Jahrb. XIV. Abth. I. Morph. g 



