Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 7^ 



more than, through the membrane that closes the orbital opening 

 of the brain case. The trochlearis pierces the orbital membrane 

 dorso-lateral to the opticus, at its extreme lateral edge, lying, as it 

 issues, at the apex of the large reentrant angle in the antero- 

 mesial edge of the alisphenoid. This apex of the angle, which is 

 rounded, is accordingly the partly formed foramen of the nerve 

 (trfr). A blood vessel perforates the bone near its antero-mesial 

 edge, slightly dorso-anterior to the trochlearis notch. The fora- 

 men (acz'fr) is an exceedingly small one, and corresponds in posi- 

 tion to the foramen that, in Amia, transmits the anterior cerebral 

 vein. No attempt was made to trace the vein in Scomber. 



Between the antero-ventral corner of the alisphenoid, the lateral 

 edge of the basisphenoid and the anterior edge of the petrosal, 

 there is a relatively large foramen (ocuifr), through which the 

 nervus oculomotorius leaves the cranial cavity and enters the ex- 

 treme anterior end of the eye-muscle canal. 



The Basisphenoid (BS) of Scomber, is, as in most teleosts, 

 a small, median, Y-shaped bone. The shank of the Y is thin, 

 slender and slightly curved, and lies nearly vertically in the mid- 

 dle plane of the head. Its upper and lower ends turn slightly 

 backward, the latter end being strongly attached to the dorsal sur- 

 face of the parasphenoid in a slight, median depression of that 

 bone, about opposite the anterior edges of its lateral wings. The 

 depression usually lodges a tiny bit of cartilage, which represents 

 a small remnant of the cartilaginous interorbital septum. The 

 arms of the bone are much broader and stronger than the shank. 

 They project laterally and slightly upward, and lie in an inclined 

 position, their flat dorsal surfaces being presented upward, back- 

 ward and mesially. Their outer ends are about twice as wide as 

 their bases, are serrated, and connect by suture, on each side, with 

 the alisphenoid and petrosal. In the middle of the outer edge of 

 each arm, usually directly opposite the sutural line between the 

 alisphenoid and petrosal, there is a deep, rounded indentation, 

 which forms, with the adjoining bones, the foramen for the ner- 

 vus oculomotorius. This foramen varies slightly in position in 

 diflferent specimens, and is said by Stannius (No. 70, p. 16) to lie 

 in the " Knochernen Keilbeinfliigel." 



