THE SKULL AS A WHOLE 



173 



former occupy a general position between the orbits, while the 

 latter are interposed between the frontal bones and the occipital 

 segment. A small portion of the roof is formed posteriorly, how- 

 ever, by an unpaired, lozenge-shaped element, the interparietal 



ppm. 



,js.m 



I p.o.e. so 

 f.m.o. 



Fig. 87. \'entral surface of the skull: .\S, alisphenoid (ala magna); _B, 

 basioccipital (basilar portion of occipital); BS, basisphenoid (body of posterior 

 sphenoid); EXO, exoccipital; M, maxilla; PL, palatine; PMX, premaxilla; 

 PR, presphenoid (body of anterior sphenoid) ; SO, supraoccipital (squamous 

 portion of occipital); SQ, squamosal; T, tympanic; ZY, zygomatic. 



ch, choana; c.hy., hypoglossal canal; c.o., occipital condyle; f.c.e., external 

 carotid foramen; f.in., incisive foramen; f.j., jugular foramen; f.l., foramen 

 lacerum; f.m., mandibular fossa; f.m.o., foramen magnum; f.p.m., greater 

 palatine foramen; f.s.a., anterior sphenoidal foramen; m.a.e., osseous portion 

 of external acoustic meatus; p.j., jugular process; p.o.e., external occipital 

 protuberance; p.pl., palatine process of maxilla; p.pm., palatine process of 

 premaxilla; p.pt., medial and lateral laminea of pterygoid process of posterior 

 sphenoid; s.m., spina masseterica. 



bone, and by the shield-shaped projection, described above, which 

 is part of the occipital bone. 



The facial portion of the skull is constituted largely by the invest- 

 ing bones of the upper jaw, palate, and mandible, but it encloses 



