73J THE SKULL OF AM lURUS— KINDRED 73 



ethmoid (Fig. 7). The posterior spicules of the supraethmoid are inserted 

 in grooves on the ventral surface of the parasphenoid. The anterior lateral 

 margins of the bone, fitting tightly against the cartilage of the ethmoid plate, 

 are separated from the ectethmoids by a narrow interval. Posterior to the 

 supraethmoid, the orbitosphenoid is developed between the parasphenoid and 

 the chondrocranium. In this region the parasphenoid is limited to the ventral 

 surface of the orbitosphenoid; the arcus palatini muscles are inserted in a gioove 

 on each side of the former. The projection ventral to this groove ends pos- 

 teriorly in a little knob ventral to the trigemino-facial foramen (Figs. 6, 20). 

 At the posterior end of the orbitosphenoid the parasphenoid expands laterally 

 to form the posterior margin of the optic foramen, interdigitating dorsally with 

 the ahsphenoid. Behind the ahsphenoid the parasphenoid interdigitates with 

 the prootic and with it forms the ventral posterior margin of the trigemino- 

 facialis foramen. The posterior end of the parasphenoid is inserted in grooves 

 on the ventral surface of the basioccipital. 



Behind the orbitosphenoid, the parasphenoid is excluded from the floor of 

 the cavum cranii by the suprasphenoid. In the younger stage the supra- 

 sphenoid develops on the cerebral surface of the parasphenoid and is firmly 

 connected with it, even in the 32 mm. stage (Fig. 32). There are spaces in 

 the floor of the craniiun close behind the orbitosphenoid between the para- and 

 suprasphenoid in the adult which show where the cartilage has been resorbed 

 (Fig. 7), but traces of cartilage are present also. Sagemehl, in his tudy of the 

 Characinidae and the Cyprinidae, did not recognize a suprasphenoid element 

 anchylosed to the cerebral part of the parasphenoid, but described the floor 

 of the cavum as formed by the parasphenoid. It is evident that, had he 

 studied the development of this region, he would have identified two elements 

 in the composition of his parasphenoid. He states that in the Cyprinidae the 

 parasphenoid forms the posterior end of the interorbital septum when such is 

 present. In all of the other teleosts, as Salmo, with a medium sized interorbi- 

 tal septum, the part of the septum posterior to the optic foram na and anterior 

 to the hyopophysis is formed by a Y or T-shaped suprasphenoid (basisphenoid 

 of the usual terminology). The parasphenoid always forms the support of 

 the basal part of the Y. In Amiurus there is no basal part to the Y, consequently 

 the arms He directly upon the cerebral surface of the parasphenoid and it is 

 only by the study of the development of this region that the two elements are 

 recognizable. Even in the adult the two elements are recognizable to a certain 

 degree in the median section of the cranium (Fig. 7), where the posterior end 

 of the orbitosphenoid and the anterior end of the prootic are enclosed by the 

 parasphenoid externally and the suprasphenoid internally. 



In those fishes which have a well developed eye-muscle canal — Salmo, Scom- 

 ber, and the Loricati — the parasphenoid is separated from the prootic bones 

 by the lumen of the canal, the floor and part of the side walls of which are 

 formed by the parasphenoid. In Amiurus the parasphenoid is fused to the 



