320 



SKELETON OF THE HOESE. 



bones are known as occipital bones (fig. 186, So, Ex.0, Bo), of 

 which there are several ; these are perforated by a large round 

 hole, the foramen magnum, out of which passes the portion of 

 the brain, the medulla oblongata, connecting the former with the 

 spinal column. Beneath this opening are the two swellings, the 

 occipital condyles. The top of the cranium is composed of four 

 flat thin bones : the ones joining the occipitals are the imrietal 



Fig. 18(i.— Diagram op the Relations of the Principal Bones of 

 THE Mammalian Skull. 



Me, Mesethraoid ; Ps, presplienoid ; Bo, basioccipital ; Bs, basisphenoid ; Os, orbito- 

 sphenoid; Fr, frontal; Ex.0, exoccipital; SO, supraoccipital ; Na, nasal; Turh, tur- 

 binals ; Per, periotic ; 1, poaition of exit of olfactory nerve ; 2, optic nerve ; 3, motoi' 

 oculi nevve; 4, trochlear nerve; 5, 7, 8, three divisions of 5th nerve; 6, abducens 

 oculi; 9, facial; 10, auditory; 11, glosso-pharyngeal ; 12, pneumogastric ; 13, spinal 

 accessory; 14, hypoglossal; Sg, squamosal; Ty, tympanic; Vo, vomer; P.Mx^ pre- 

 raaxilla; Mx, maxilla; PI, palatine; Pt, pterygoid; Ju, malar; la, lachrymal; M, 

 mandible; ilf/c.C, MeL-kel's cartilage ; iv, anterior hyoid arch ; v, posterior hyoid arch. 

 (After Flower.) 



bones (P (fig. 186) and Pa (fig. 186)), and those in front of the 

 parietals are the frontaU (F and Fr) ; these extend behind the 

 eye-regions. The sides of the skull are partly shut in by the 

 temjyoral hones with the zygomatic processes {Z and 8q). 



The sphenoid bones {As, Ch, Ps, and Bs) shut in the side 

 of the cranium partly, and lie between the occipitals, frontals, 

 palatine (PI), vomer (Fo), pterygoid {Pt), ethmoid, and temporals. 



