PRIMORDIAL CRANIUM OF THE CAT 385 



straight direction of the preoptic, it presents a marked bend, convex 

 caudally. This curve is apparent to a slight extent in the bony 

 cranium. Judging from figures of the chondrocranium of several 

 manmaals, the bend in question seems to be a characteristic of this 

 cartilaginous rod. In cat the knuckle of the curve apparently mark 

 the place of union of the metoptic process of the trabecular plate 

 and the corresponding process of the ala orbitahs. Opposite this 

 spot the oculo-motor nerve leaves the cranium by the orbital fissure. 

 What significance there is in the form and relations of the metop- 

 tic root, which are early estabUshed and permanently retained, 

 must await future inquiry. 



Ethmoidal region 



Region of the olfactory fenestra. The floor of the condrocranium 

 of mammals, between the levels of the preoptic root of the ala 

 orbitahs and the fenestra olfactoria, is made by the lamina infra- 

 cribosa, which is the roof of the posterior cupola of the nasal cap- 

 sule and an extension of the planum antorbitale. The lateral 

 brancl^ of the naso-cihary nerve runs upon this lamina on its way 

 toward the interior of the nasal capsule, having come through 

 the spheno-ethmoidal fenestra from the orbit. The lamina cri- 

 brosa, a structure peculiar to mammals, develops over the fenes- 

 tra olfactoria. Now, in reptiles the ethmoidal nerve and the • 

 whole of the posterior cupola, with the olfactory fenestra, are 

 extracranial. A study of these contrasting conditions of the mam- 

 malian and reptilian ethmoidal skeletons has led- Gaupp to the 

 conclusion that a new region, named by him recessus supracri- 

 brosus, has been added to the mammalian brain case, and that 

 this region is comparable, in reptiles, with the extracranial parts 

 about the olfactory fenestra. In the cat, the form and relations 

 of the posterior cupola and olfactory fenestra are essentially as 

 in other mammals. The fenestra olfactoria opens directly into^ 

 the chondrocranial cavity. As aheady stated, the lamina cri- 

 brosa was not present in the stages of the cat studied, conse- 

 quently no data have been presented bearing on the question of 

 its position relative to the walls of the chondrocranium. The 



