288 SKELETON OF THE EABBIT 



On the inner surface of each ramus, just 

 behind the grinding teeth, is the inferior 

 dental foramen, through which the mandi- 

 bular nerve enters to supply the teeth. 



4. The hyoid bone lies in the floor of the hinder part of 



the mouth, between the rami of the mandible. 



It consists of a median body, and two pairs of 

 backwardly projecting cornna, of which the posterior 

 are the larger. 



The anterior cornua are the ventral ends of the 

 hyoidean arches, the dorsal ends of which are 

 probably represented by the stapes : the posterior 

 cornua are the lower ends, and only persistent parts, 

 of the first pair of branchial arches. 



5. Apertures on the surface of the skull. 



After the several bones have been examined, the 

 positions of the more important foramina should be 

 determined, most of which have already been seen. 

 Except when otherwise stated, the several apertures 

 are paired. 

 a. Foramina for the passage of cranial nerves. 



i. The optic foramen is a large round median hole 

 in the orbito-sphenoids : it puts the two 

 orbits in communication with the crania; 

 cavity and with each other, and transmits the 

 optic nerves, 

 ii. The foramen lacerum anterius, or sphenoidal 

 fissure, is a vertical slit below and behind the 

 optic foramen, and between the basi-sphenoid 

 and ali- sphenoid. Through it the third, fourth, 

 and sixth nerves, and the ophthalmic and 

 maxillary divisions of the fifth, enter the 

 orbit from the cranial cavity. In most mam- 

 mals the maxillary division of the fifth nerve 

 leaves the skull by a separate aperture, the 

 foramen rotundum, which in the rabbit is 

 confluent with the sphenoidal fissure. 



