290 



SKELETON OF THE HOKSE. 



bones are known as occipital bones (fig. 153, So, Hx.O, 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 parietal 



Fig. 153. — Diagram or the Relations of the Principal Bones of 

 THE Mammalian Skull. 



Me, Mesethmoid ; Ps, prespheuoid ; Bo, basioccipital ; Bs, basisphenoid ; Os, orbito- 

 sphenoid; Fr, frontal; Ex.0, exoceipltal; SO, supraocclpital ; Na, nasal; Turh, tur- 

 binals ; Per, periotic ; 1, position of exit of olfactory nerve ; 2, optic nerve ; 3, motoi: 

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

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

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

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

 mandible ; Mh.C, Meckel's cartilage ; iv, anterior hyoid arch ; v, posterior hyoid arch. 

 (After Flower.) 



bones (P (fig. 152) and Pa (fig. 153)), and those in front of the 

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

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

 tempoml hones with the zygomatic processes {Z and Sq). 



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

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

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



