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With the human skull I have already attempted, in an earlier work f97b), to compare the 

 condition found in Amia, and certain conclusions there arrived at can be repeated here with additional 

 facts in their support. 



In Man (Quain '92/96), the Gasserian ganghon lies in the cavumMeckelii,that cavum being said 

 to be a recess in the dura mater whieh oecupies a depression on the upper surface of the petrous 

 portion of the temporal bone. But this so-called recess must be a space in the dura mater and not 

 a simple recess on its cerebral surface; for elsewhere in the same work the Gasserian ganghon is said 

 to lie between the inner and outer layers of the dura, the inner one of these two layers being the 

 primitive, single-lavered dura, and the outer one being the endocranium, or internal periosteal mem- 

 brane of the skull. The fusion of these two separate membranes of embryos is said to form the double- 

 layered dura of the adult, the Gasserian ganglion being, in this process, enclosed between the two 

 layers. The internal part of the cavum Meckelii is said to come into close relations with the posterior 

 extremity of the cavernous sinus, that sinus also being a space between the two layers of the dura 

 of the adult, and the sinuses of opposite sides being in communication by means of the intercavernous 

 sinuses. Between the cavernous sinuses of opposite sides, in a median depression on the dorsal sur- 

 face of the dura, lies the pituitary body. The cavernous sinuses each receive the Ophthalmie vein 

 anteriorlv, these veins communicating with each other across the middle line by means of the inter- 

 cavernous sinuses, and discharging their blood posteriorly into the petrosal sinuses. The inter- 

 communicating veins are accordingly the homologues of the pituitary veins of my descriptions of 

 fishes, and the cavernous sinuses, intercavernous sinuses, and Cava Meckelii are together the appa- 

 rently strict homologues of the myodome of Amia; that myodöme consisting, as I have already ex- 

 plained, of a ventral portion which is the homologue of the myodome of teleosts, and an upper lateral 

 Chamber, on either side, which is the homologue of the trigemino-facialis chamber of teleosts. 



The outer wall of each cavernous sinus is traversed by the oculomotorius, trochlearis and ab- 

 ducens nerves, by the Ophthalmie and superior maxillary branches of-the trigeminus, and by the 

 internal carotid artery. Having traversed the wall of the sinus, the oculomotorius, trochlearis, 

 abducens and ophthalmicus trigemini all issue into the hind part of the orbit through the sphenoidal 

 fissure, that fissure lying between the great and small wings of the sphenoid bones, the former of 

 which is said to be formed by the alisphenoid bone and the latter by the orbitosphenoid. The fissure 

 is also traversed by the Ophthalmie vein as it passes from the orbit into the cavernous sinus. The 

 sphenoidal fissure thus corresponds in every detail, excepting in that it transmits the ophthalmicus 

 trigemini, to the orbital opening of the myodome of Amia. But the fissure lies, in man, between 

 the alisphenoid and orbitosphenoid bones, instead of between the parasphenoid and basisphenoid 

 legs of the alisphenoid. This howeve]* seems unmiportant, for, as I have also pointed out ('97b), 

 the so-called basisphenoid of Amia is probably simply a part of the orbitosphenoid, ossifying from 

 a separate and independent center; the orbitosphenoid of Amia and Man invading a region that 

 is ossified as part of the alisphenoid in teleosts. Regarding the ophthalmicus trigemini, which tra- 

 verses the sphenoidal fissure in man, that nerve is the homologue of the ophthalmicus profundus 

 of fishes, a nerve not found in Amia or teleosts, but as it arises from the profundus ganglion it would 

 probably issue from the skull with the ciliaris profundi, which latter nerve traverses the orbital 

 opening of the myodome. 



The foramen rotundum and the foramen ovale both perforate, in man, the great wing of the 

 sphenoid, and transmit respectively the superior and inferior maxillary branches of the trigeminus, 



Zoologica. Heft 57 25 



