45S 



CHORDATA 



The cartilage bones can be divided according to the cranial regions 

 into four groups: (i) bones of the hinder part of the hend—oalpitalij; 

 (2) bones of the ear region— oZ/cj; (3) l^t-ines near the eye—splioioiihilia; 

 and 4) of the nasal capsule— f///;»('/</j//j. The occipital a— four in 

 number (,ligs. 310-5181— united in the higher mammals to a siiigle occip- 

 ital bone, surround {he fordiiicn ;«jt;«7n», the opening through which the 

 spinal cord passes to connect with the brain. They are a pair of f.v- 

 ocnpilals, right and left, a siiprdoi-cipital al>ove and a hasioaipilal below. 

 The otica depend in their development upon the extent of the otic region. 

 In the tishes (fig. 510) where this part is large, several bones may pre- 

 sent: t-piotic, ptcrolii, sphaiotic, proolic, and often opistholic. In the 

 mammals, on the other hand, these are fused to a single pclrosal bone 

 (figs. 517-519) of small size. 



Fig. 517. — Skull of goat (from CbusV .1/s, ,ilisphcnoiil; Ps, h,isisphenoid: C, 

 occipital con(.h"le; EIli, niesethnioiil, co\'ering the cctclhnioicl; Fo, optic foramen in 

 orbitosphenoici; Fr, frontal; /;/lv, ]iremaxiUar\-; //), interparietal; Jti. iiigal (malarV, 

 La. lacrimal; .l/.v, maxillary; A'<;, nasal; Oh, basiocci]iital; Ol, exocci|iilal; Ors, orbito- 

 sphenoid; Pa, parietal; Pal, palatine; Pr, petn~>sal; Pm, jiaramasloid process; Ps, pre- 

 sphenoid; Pt, pter\"goid; 5/', frontal sinus in frontal bone; Spl>. basisjihenoid; Sc/, squa- 

 mosal; Ty, tympanic; \'o, \omer. 



The line of the basioccipital is continued forward by the unpaired 

 elements of the sphenoidalia, a basisphcnoiJ behind and a prcsphcnoid 

 in front. With each is connected, right antl left, a pair of bones; with the 

 basisphenoid tlie alisplicnoids, with the presphenoid the orbilosphciioicis, 

 just as the exoccipitals Hank the liasioccipital. In the region of the nasal 

 capsule there is an unpaired mcsiilnnoid with a pair of eclclhmoids. Hence 

 tlae cranium of primary bones may be described as a chain of four median 



