290 



SKELETON OF THE HORSE. 



bones are known as occipital bones (fig. 153, 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 

 fiat thin bones : the ones joining the occipitals are the parietd 



Fia. 153. — Diagram of the Relations of the Principal Bones of 

 THE Mammalian Skull. 

 Me, Mesethmoid ; Ps, prespheuoid ; £0, basioccipitel ; £s, liasisphenoid ; Os, orbito- 

 Hplienoid; Fr, frontal; Ex.0, exoccipital ; .SO, supraoccipital ; Na, nasal; Twi, tur 

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

 oculi nerve ; 4, trochlear nerve ; 5, 7, S, tliree divisions of 5th nerve ; 6, abducens 

 oculi; 9, facial; 10, auditory; 11, glosso-phai-j'ngeal ; 12, pneumOL.'astric ; 13, spinal 

 •accessory ; 14, liypoglossal ; Sq, squamosal ; Ty, tympanic ; Vo, vomer ; PMx, pre- 

 maxilla; Mx, maxilla; PI, palatine; Pt, pterygoid; /k, malar; La, lachrymal; U, 

 mandible ; Mk.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 frontah {F and Fr) ; these extend behind the 

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

 temporal 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 (Pi), ethmoid, and temporalsi. 



