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ORBITOSPHENOID. 



There is no orbitosphenoid. 



ALISPHENOID. 



The alisphenoid is sub-oval in outline. Its dorso-anterior third or half is overlapped externally 

 by the posterior portion of the ventral process of the frontal. Its dorsal edge is capped with cartilage, 

 and this cartilage rests against the ventral surface of the frontal immediately internal to the ventral 

 process of that bone. The anterior edge of the bone is presented mesially and but slightly forward, 

 and suturates with the ventral flange-like process of the frontal. Its posterior edge is presented laterally 

 and but slightly backward and is bounded, in its dorsal portion, by the sphenotic and the body of 

 the proötic, but is separated from both of those bones by a line of cartilage. The ventro -posterior 

 corner of the bone suturates, without intervening cartilage, with the dorso-anterior edge of the 

 prepituitary portion of the mesial process of the proötic and with the antero-lateral corner of the 

 body of the basisphenoid. Its ventral edge forms part of the boundary of the orbital opening of 

 the brain case and gives attachment to the membranes that, in the recent state, close that opening. 



On the internal surface of the alisphenoid, near its anterior edge, a ridge runs downward a 

 short distance from the dorsal edge of the bone. This ridge is continuous with a similar ridge on the 

 corresponding surface of the cartilage that caps the bone, and is also continuous with, or is slightly 

 overlapped by, the little ridge and process, already described, on the ventral surface of the frontal. 

 The entire ridge thus formed, forms the posterior boundary of what I have referred to as the fore- 

 brain recess of the cranial cavity, that recess thus lying mainly anterior to the alisphenoid, and the 

 alisphenoid bounding the mid-brain region. 



A small foramen is always found perforating the alisphenoid, and the ventral edge of the 

 bone, where it bounds the orbital opening of the brain case, is always notched to form an imperfectly 

 closed and larger foramen. The small foramen transmits a small nerve accompanied by two small 

 arteries; the nerve being a branch of the ophthalmicus lateralis destined to innervate organ 6 of the 

 supraorbital canal, but accompanied by other fibers, probably general cutaneous, and the arteries 

 being, one a branch of the external carotid and the other a branch of a blood vessel to be later 

 described as the vessel x and that would seem to represent, in part at least, the hyo-opercularis 

 artery of my descriptions of Amia. The notch in the ventral edge of the bone transmits the nervus 

 trochlearis. Dorso-anterior to this notch, and close to it, a smaller notch transmits a branch of the 

 orbito-nasal vein. In Amia, this small vein perforates the alisphenoid, and in my descriptions of that 

 fish I called it the anterior cerebral vein. In Scomber a corresponding foramen was found in the 

 alisphenoid, and I assumed that it transmitted a corresponding vein, as it doubtless does. In 

 Ophiodon, Allen ('05) does not describe this vein, but it would seem as if it must there be found 

 for I find it in Cottus, Trigla, Peristedion and Dactylopterus as well as in Scorpaena, but per- 

 forating the alisphenoid in all those fishes instead of passing across its anterior edge. It would 

 seem, even, to have a certain morphological importance, though what it may be I can not yet de- 

 termine. It, or the foramen that transmits the branch of the external carotid, or these two fora- 

 mina together, may perhaps represent the foramen spinosum of human anatomy. 



On the outer surface of the posterior portion of the alisphenoid, and extending to its ventral 

 edge, there are two more or less developed ridges. The postero-lateral one of these two ridges is often 

 wholly wanting, the antero-mesial one being present, more or less developed, in all my specimens. The 



