76 ILLINOIS BIOLOGICAL MONOGRAPHS [76 * 



frontal. The inner ends of the canals for the ophthalmic branches of the fifth 

 and seventh nerves have been discussed above. McMurrich noted both of 

 these canal openings, but only one nerve. He stated (1884b) that the upper 

 opening "opens into the interior of the bone like other similar foramina which 

 perhaps, have a nutritive unction." In reality this foramen is the posterior 

 end of a canal for the passage of the ophthalmicus branch of the facial nerve 

 and not for a blood vessel. He also says that the ventral margin of the ali- 

 sphenoid bone articulates with the basisphenoid (suprasphenoid, auct.) alone 

 and does not touch the parasphenoid, but from a study of sections through 

 this region, I think that para- and suprasphenoids are fused along the ventral 

 margin of the bone and that the external surface is the parasphenoid and the 

 internal, the suprasphenoid. I cannot find any point where aHsphenoid meets 

 the prootic as he maintains, but since this is common in most of the teleosts, 

 there is a possibility that such was the condition in the specimens he studied 

 although it is present in none of mine. 



An historical review of the various names which this bone has borne since 

 the earliest descriptions of it by Meckel, Arendt, Cuvier, and others, is given 

 by Owen (1848), Vrolik (1873), and Starks (1901). Since the orbitosphenoid 

 was lacking in the perch, which Cuvier used as his type, he caused confusion in 

 the literature by regarding the alisphenoid as the homologue of the ala orbi talis 

 and the prootic as the ala magna. Halhnan (1837), as noted above, recognized 

 the true homology of the bone and called it the ala magna, because of its rela- 

 tion to the first branch of the trigeminus. Huxley's work on the homologies 

 of the basal part of the cranium helped to define the criteria for the identifica- 

 tion of the bone as it is known today. Owen, at the same time, ignored Hux- 

 ley's conclusions and regarded the bone as the orbitosphenoid because of its 

 relation to the optic nerve. At present all ichthyologists agree that this bone 

 has approximately the same relations to the surrounding bones as has been 

 described for Amiurus and the term alisphenoid is in common use. Yet, as 

 stated above, some do not regard it as the homologue of the greater wing of the 

 mammals. 



In fishes with a well developed interorbital septum, the orbitosphenoid is 

 wanting and tlie aHsphenoid is correspondingly reduced in size. Scomber 

 (AUis, 1903), the Loricati (AUis, 1910), and Alepocephalus (Gegenbaur, 1878), 

 are good examples of this limitation in the development of the bone. In spite 

 of its size in these forms, the aHsphenoid usually encloses a small foramen for 

 the ophthalmic branch of the fifth nerve, just posterior to the optic. In 

 Megalops (Ridewood, 1904) the alisphenoids meet in the roof of the cranium. 

 In Gasterosteus (Swinnerton, 1902) the aHsphenoids are lacking, their place 

 being taken by dorsal spiculae of the parasphenoid. 



The Cyprinidae (Sagemehl, 1891) approach nearest to the type of aHsphe- 

 noid found in Amiurus, and in Catostomus there is the same anterior projection 

 of the bone. Stannius (1853) recognized this high development of the aH- 



