10 ILLINOIS BIOLOGICAL MONOGRAPHS [180 



the parasphenoid, allows the passage of the anterior cerebral vein, the 

 ciliary artery, and the ciliary nerve. Allis ( '09) found a small foramen 

 for the anterior cerebral vein perforating the alisphenoid in Scomber, 

 Cottus, Trigla, Peristedion, Dactylopterus, and Scorpaena and states 

 that Allen (1905) did not describe it in Ophidon. I do not find a 

 foramen perforating the alisphenoid in Ophidon nor in Scorpionichthys. 

 The anterior cerebral vein, according to Allen (1905), passes through 

 the foramen formed by the prootic, the ' dorso-lateral process of the 

 parasphenoid, and the posterior edge of the alisphenoid. 



Parasphenoid. — The parasphenoid (Fig. 6, ps) is the longest 

 bone of the skull and forms the ventral surface of the entire length of 

 the cranium with the exception of the process of the vomer which passes 

 caudad into the parasphenoid. The anterior portion is almost perfectly 

 straight on the ventral surface while the posterior portion is slightly 

 curved upward and the edges of the bone turn up dorso-laterally, the 

 entire length of the bone. In the middle portion the edge projects 

 upward as a long process which extends dorso-laterally to the edge of 

 the alisphenoid. Directly posterior to the process, in the angle between 

 it and the prootic, is a foramen through for the internal carotid artery. 

 The bone has a concave longitudinal groove the entire length of the 

 dorsal surface which, in the anterior portion, is divided by a tall parti- 

 tion, extending from a point immediately anterior to the tall processes 

 to the anterior end of the bone where it terminates in the ethmoid and 

 the vomer. At the anterior end there is a V-shaped slit on the ventral 

 edge for the postero-ventral process of the vomer. The posterior end 

 also has a V-shaped slit extending cephalad, forming the posterior 

 opening of the myodome. The dorsal surface of the posterior portion 

 forms a part of the floor of the myodome, between the prootics and the 

 two tall dorso-lateral processes of the bone itself. This portion also 

 forms a support for the prootics and the basioccipital. 



Basisphenoid. — The basisphenoid (Fig. 6, hs) is a T-shaped 

 bone forming the anterior part of the roof of the myodome, being at- 

 tached to the processes extending mesad from the prootic, just postero- 

 ventrad to the alisphenoid. The pedicle is curved ventro-cephalad to 

 the parasphenoid where it is united to it by a bulb of cartilage. It is 

 laterally flattened and the rest of the bone between the prootic processes 

 is dorsally flattened but rounded ventrally and slightly curved cephalad 

 at the point where the pedicle process projects. 



Pterotic. — The pterotics (Figs. 1, 6, pto) form the lateral edges 

 of the dorsal surface of the skull, posterior to the sphenotics and the 

 postfrontals, and also the lateral borders of the temporal fossa. On the 

 dorsal edge of such there is a narrow ridge extending from the anterior 

 end to beyond the middle from which the surface gradually slopes to 



