92 ELEMENTAR Y ANA 7V M I : [LESS. 



very obtuse angle, while with the cribriform plate it forms an 

 obtuse one, open downwards and forwards. 



The extreme length of the cranial cavity is always more 

 than 2] times that of the basi-cranial axis, while it may be 

 nearly 2f times the length of the latter. 



The half of the lower jaw forms an arc joining the skull 

 above directly at the glenoid surface. 



The half of the hyoid bone forms a much smaller arc 

 behind the former, and joined to the skull indirectly, namely 

 by the ligament which suspends it by the corniculum from 

 the styloid process. 



When the skull is divided vertically through the external 

 auditory meati, i.e. transversely, or in the direction of the 

 coronal suture, we see that the basilar part of the occipital 

 forms as it were a centre. 



The anterior part of the section shows the great cranial 

 arch rising above this centre and closed in front, while below 

 it is the arch of the lower jaw, and further forward the arch 

 of the upper jaw, enclosing the double tube of the nostrils 

 which extends from the anterior to the posterior nares. 



The posterior part of the section shows us the hinder part 

 of the great cranial arch rising above the centre and closed 

 behind, while below it is the arch of the hyoid and its liga- 

 ments, reaching up to the styloid processes. 



16. As to the CAVITIES OF THE SKULL : the orbits in man 

 are pyramidal cavities completely encircled by bone, and 

 each so separated off from the temporal fossa behind it, 

 by the malar and alisphenoid, that the elongated spheno- 

 maxillary fissure is the only opening left. 



At the back are the optic and round foramina, and between 

 them the sphenoidal fissure, the vidian foramen being hidden 

 from view. 



Within the anterior margin on the inner wall of each orbit 

 is the lachrymal foramen. 



The two orbits are separated from each other in part by the 

 cranial cavity (above the cribriform plate), and in part by the 

 nasal cavity (below the cribriform plate). 



The nasal fosses, extending backwards above the palate 

 from the anterior to the posterior nares, and enclosed be- 

 tween the maxillae, are separated from each other by the 

 median, ethmoid, and vomer, and in front of these by carti- 

 lage. The three turbinals project inwards from the outer 

 wall of each fossa, and beneath the lowest the inferior ter- 

 mination of the lachrymal canal opens. 



