980 W. K. GREGOKY REPORT OF COMMITTEE ON NOMENCLATURE 



Apocla, which I believe are real exposures of the sphenethmoid in the one 

 and of the ^^ethmoid^^ in the other case. 



OrJj it sphenoid and AUsphenoid. — The orbitosphenoid of a mammal is 

 a cartilage ossification in the ala orbitalis ; the pair of ossifications either 

 spread down into the lamina infra-cribrosa and through the basal plate 

 of the orbitotemporal region or there is an independent center of ossifica- 

 tion for the presphenoid in this region. In Monotremes the ala orbitalis 

 lies entirely in advance of the optic nerves. In some types — for example, 

 Sus and Perameles — the basal plate of the orbitotemporal region and the 

 pres])he]ioidal area is largely formed by the posterior end of the septum 

 nasi. When this is the case, it is apparently obvious that the ala orbitalis 

 is homologous with Gaupp's planum supraseptale of the lizard skull, 

 which is connected with the tectum synoticum by the taenia marginalis, 

 just as the ala orbitalis is by the commissura orbitoparietalis. 



Professor Willi ston's lizard bone* was correctly described by Cuvier, 

 who says that it is the only representation in lizards of the Cxbito- and 

 alisphenoids of mammals. I do not yet know exactly how and when it 

 ossifies, but it does seem to be a cartilage bone, perhaps ossifying in the 

 bar separating the fenestrge metoptica and optica. If so, although analo- 

 gous, it will not be homologous with the orbitosphenoid. As a matter of 

 fact, there are usually three other calcifications in this region of the lizard 

 skull — one in the septum, extending up to the brain-case, the others in 

 the wall of the brain-case — but these are not apparently real bones. There 

 is no evidence extant as to the mode of ossification of the ''^alisphenoid'^ 

 of the crocodile, but I fancy from its relations it is probably homologous 

 with Williston's lizard bone. 



Bland Sutton many years ago showed that the cranial cavity of a mam- 

 mal is not homologous with that of a lizard, because in the first case the 

 Gasserian ganglion is inside the skull and in the other it lies outside, be- 

 tween the skull wall and the epipterygoid. Gaupp rediscovered this and 

 called the space in which the ganglion lies in mammals the cavum epi- 

 ptericum. In Monotremes there is a strong membrane separating this 

 cavity from that for the brain — the taenia clinoorbitalis — and a cartilag- 

 inous nodule lying in front of the prootic notch, which I found in Platy- 

 pus, lies in this membrane. It therefore follows that this membrane and 

 its included cartilaginous elemxcnts is the original wall of the reptilian 

 cranial cavity, with which it agrees in all relations, including the general 

 distribution of nerve- exits. 



Hence the mammalian alisphenoid can not be homologous with any 



*Am. Jour. Anat, vol. x, p. 79. 



