Chap. VIII.] THE SKELETON. 143 



the sides of the brain-case two other bones are affixed to the 

 exterior. These are (1) the squamosal (sq.), which fills the 

 anterior part of the lateral gap, and separates the ali-sphenoid 

 from the parietal ; and (2) the tympanic, which forms a swollen 

 rounded mass (tympanic bulla, 45, t. b.) stuck on to the outer side 

 of the periotic. 



The brain- case thus constituted has the following foramina 

 (see Fig. 44, A.): 



1. Olfactory ; numerous perforations in the cribriform plate for 

 the fibres of the first nerve. 



2. Optic ; for the second nerve, just within the orbito-sphenoid. 

 The confluence of the optic foramina places the orbits in com- 

 munication. (This is not so in the dog or cat.) 



3. Sphenoidal (or foramen lacerum anterius) ; between the 

 basi-sphenoid and ali-sphenoid. It transmits the third, fourth, 

 sixth, and first and second divisions of the fiffh nerve. (In the 

 dog or cat the second division of the fifth passes through a 

 separate orifice, the foramen rotundum.) 



4. Foramen lacerum medium; for the third division of the 

 fifth nerve and the internal carotid artery. It lies between the 

 periotic and the ali-sphenoid. (In the dog or cat the third 

 division of the fifth nerve passes through a separate orifice in 

 the ali-sphenoid, the foramen ovale.) 



5. Facial ; this passes through the periotic bone, and emerges 

 by a foramen (styto-mastoid\ behind and above the swollen 

 portion of the tympanic. It transmits the seventh nerve. 



6. Auditory ; the eighth nerve enters the periotic close to the 

 seventh, the shallow depression common to the two being the 

 internal auditory meatus. Near it is a deeper depression, the 

 floccular fossa. 



7. Foramen lacerum poster ius ; between the periotic and ex- 

 occipital, for the transmission of the ninth, tenth, and eleventh 

 nerves. 



8. Condylar ; in the occipital bone ; two small apertures for 

 the twelfth nerve (one in dog or cat). 



9. Magnum, within the occipital ring, for the spinal cord. 



It is a fact worth remembering that the three main segments of 



