THE SKULL. 21 



over by the arches already mentioned (24). In 

 it, just above the inner side of the proximal 

 end of the quadrate bone, is the large foramen 

 through which the superior and inferior maxil- 

 lary divisions of the fifth cranial nerve leave the 

 skull (190, 191). 



28. Note that the anterior end of the brain-case 

 proper is not inclosed by bone, but opens widely be- 

 tween the orbits ; also, that between the orbits there is 

 no bony partition, the inter-orbital septum being nearly 

 entirely membranous, and usually removed in cleaning 

 the skull. In the middle line between the orbits and 

 close to the bone bounding them below, will, however, 

 be found the naso-ethmoidal cartilage, passing out from 

 the interior of the skull-chamber and there flattened 

 dorso-ventrally ; between the orbits it becomes cylin- 

 drical, and then, farther forward, expands into a verti- 

 cal plate {mesethmoid), which enters the nose and forms 

 most of the partition between the nostrils. 



29. The floor of the orbit is not completely bony, but 

 presents a considerable fontanelle, closed in the recent 

 state by membrane : through this a branch of the su- 

 perior maxillary nerve will subsequently (190) be found 

 to pass. 



30. On the posterior boundary of the nares, note a 

 round aperture above the mesethmoid cartilage, and 

 close to the roof of the nose. Into it, in the recent 

 state, reached an anterior prolongation of the brain, en- 

 veloped in dura mater (169), which passed out of the 

 large anterior opening of the proper brain-case above 



