THE SKELETON 45 



The interparietal is a triangular bone situated at the junc- 

 tion of the two parietals and occipital bones. Its sutures are 

 usually obliterated quite early. 



The occipital (Figs. 17, 18, and 19) is a single bone sur- 

 rounding the foramen magnum and articulating with the inter- 

 parietal, parietals, temporals, and sphenoid. In the young 

 kitten it is composed of four parts: the supraoccipilal, lying dor- 

 sal to the foramen magnum, the two exoccipitals, lying laterad 

 of it, and a basioccipital, bounding it ventrally. The cres- 

 centric elevation on the iupraoccipital near its parietal margin 

 is the la mbdoidal ridge, to which several muscles are attached. 



The exoccipitals bound the cerebellum laterally and sup- 

 port the occipital condyles, which articulate with the atlas or 

 first vertebra. Immediately caudad of the bulla is the jugular 

 process. There are two foramina, one of which, the hypo- 

 glossal canal, opens ventrally with the jugular foramen adja- 

 cent to the bulla, while the other, the condyloid canal, opens 

 more dorsally at the side of condyle. The former trans- 

 mits the twelfth (hypoglossal) cranial nerve, supplying the 

 larynx, hyoid bone, and tongue. The jugular foramen, or 

 foramen lacerum posterius, is at the juncture of the bulla, 

 exoccipital, and basioccipital. The internal jugular vein and 

 the ninth, tenth and eleventh nerves pass through it. The 

 basioccipital portion of this bone lies entirely on the ventral 

 aspect of the skull. It articulates craniad with the basisphe- 

 noid by a suture which is generally obliterated in cats three or 

 four years old. 



The sphenoid one lies in the center of the base of the skull. 

 It is composed of eight parts, corresponding to eight distinct 

 bones in the lower vertebrates: the basis phenoid, articulating 

 caudad with the basioccipital; two alis phenoids , extending dor- 

 sad from the basisphenoid and articulating caudad with the 

 temporals (Figs. 18 and 19) two pterygoids, projecting ventrally 

 from the basisphenoid and terminating in sharp processes; a 

 pres phenoid in the mid-ventral line craniad of the basisphenoid ; 



