No. i.] MORPHOLOGY OF THE PETROSAL BONE. 15 



parison of Jacoby's figures and descriptions of human embryos 

 (No. 1 6) with the conditions found in the adult. Gegenbaur is 

 even said by Jacoby (No. 16, p. Si) to have characterized the 

 great development of an alisphenoid bone as a peculiarity of 

 man. 



In this invasion of the sphenoidal region of the skull by dif- 

 ferent ossifications, whether in fishes or in man, the relations of 

 the nerves issuing to the several bones, as found in Amia, remain 

 remarkably constant. 



In teleosts, the opticus issues in front of or above the carti- 

 laginous, membranous, or osseous basisphenoid, between it and 

 the orbitosphenoid. The oculomotorius remains always in front 

 of the alisphenoid, but may become enclosed in the anterior 

 edge of the anterior extension of the petrosal. The trochlearis 

 lies in front of the alisphenoid, or may become enclosed in the 

 anterior edge of that bone. The profundus cannot be recognized 

 in Sagemehl's descriptions of any of the fishes examined by him. 

 In the haddock (No. 8, p. 171), what seems to be the nerve 

 issues in front of the alisphenoid; and in Amiurus (No. 19, p. 

 2/5, and No. 34, p. 366), through the alisphenoid near that 

 edge of the bone that articulates with the basisphenoid. The 

 trigeminus in the Characinidae (No. 27, p. 70) issues through 

 a single foramen in the anterior orbital part of the petrosal, its 

 relation to the alisphenoid thus being uncertain. In the Cyprini- 

 dae, the ophthalmic branch of the trigeminus issues through a 

 special foramen in the alisphenoid (No. 28, p. 568), the maxil- 

 lary branches of the nerve issuing through a foramen which lies 

 partly in the petrosal, and partly between that bone and the 

 alisphenoid. In Leuciscina and Abramidina, the latter foramen 

 is often separated into two parts by a bridge of bone; the upper 

 part of the foramen, in such cases, transmitting the trigeminal 

 nerves, and the lower part the vena ophthalmica. In the had- 

 dock and in Amiurus, the trigeminus issues with the facialis 

 through a large foramen between the adjoining edges of the 

 alisphenoid and petrosal, the foramen being often incompletely 

 separated into two or more parts by bony spicules. 



In man (No. 25, vol. ii, pt. i, p. 80), the opticus issues be- 

 tween the orbitosphenoid and presphenoid ; the oculomotorius, 



