loo THE SKULL [chap. 



These four bones surround \\\^ foramen magnuDi behind, and 

 all take share in its circumference, though the exoccipitals, 

 which bound it laterally, contribute most. On each side of 

 the foramen, and rather below than above, are the occipital 

 co?idy/es, by which the skull articulates with the first cervical 

 vertebra ; and externally to these, separated by a deep de- 

 pression, is a prominent process for muscular attachments, 

 called the paroccipital (or paraniastoid) process. The con- 

 dyles in the Dog are formed by the exoccipitals alone. The 

 part {IP) which appears to be an anterior prolongation of 

 the upper extremity of the supraoccipital, wedged in be- 

 tween the parietals, is ossified from a separate centre, and 

 in some animals remains permanently as a distinct bone. It 

 is then called interparietaL 



'Hie middle (or parietal) segment is formed by the 

 basisphenoid below. From the sides of this a pair of 

 vving-like bones {AS) extend outwards and upwards, 

 called alisphenoids ; and above these are large square- 

 shaped bones {Pa)^ meeting in the middle line above, the 

 parielals. 



The occipital and the parietal segments are in contact 

 below and above, but there would be a considerable open 

 space between . them laterally were it not for the inter- 

 position of a group of bones, which do not form part of the 

 segmented wall of the brain-case proper, but are more or 

 less connected with the organ of hearing, and will therefore 

 be described hereafter. These are the bones which, being 

 all united into one in Man, constitute the so-called temporal 

 bone of human anatomy. 



The anterior (or frontal) segment is formed by the pre- 

 sphenoid below; then by the wing-like bones {OS) projecting 

 from its sides, smaller than those of the second segment, 

 called orbitosphcnoids : and finally by two greatly expanded 



