THE RABBIT 323 



At the hinder end of the skull is the foramen magnum, a large 

 circular opening through which the spinal cord enters the brain 

 cavity. Bounding the foramen magnum on each side is the oc- 

 cipital condyle ; these condyles are a pair of protuberances which 

 articulate with the atlas and form the pivot on which the head 

 turns to the right and left. Lateral to each condyle is the long 

 pointed jugal process. At the side of the skull near its hinder end, 

 and back of the zygomatic process, is a large, round aperture, the 

 external auditory meatus, the external opening of the ear ; it com- 

 municates ventrally with a rounded and hollow expansion, the 

 tympanic bulla, which contains the middle ear. 



The anterior portion of the skull is formed of the nasal capsules 

 and the very long upper and lower jaws. The openings of the nos- 

 trils, or external nares, are at the forward end of the nasal capsules. 

 The upper jaw extends posteriorly to the orbit and bears the upper 

 incisor, upper premolar, and upper molar teeth ; its lateral side is 

 fenestrated extensively, the openings looking into the nasal cavity. 

 The lower jaw forms the whole ventral portion of the skull and 

 bears the lower incisor, lower premolar, and lower molar teeth. 

 Between the two sides of the lower jaw, and embedded in the floor 

 of the pharynx, is the delicate hyoid bone, which consists of a 

 median body and two pairs of projecting cornua, or horns ; this 

 bone is not connected with the rest of the skull, except by means 

 of muscles and ligaments, and may be lost in cleaning the skull. 



Remove the lower jaw and study the bones of the remaining 

 portion of the skull as they appear on the dorsal, the lateral, and 

 the ventral surfaces. 



The bones of the cranium, as has already been suggested, fall 

 into two categories, those of the cranium proper, or brain case, 

 and those of the special-sense capsules. Those belonging to the 

 brain case occupy the central and hinder portions of the skull-, 

 the special-sense capsules, which inclose the organs of hearing, 

 sight, and smell respectively, are membranous or cartilaginous in 

 the embryo, but certain bones develop in them which in the adult 

 animal form an intimate union with the brain case. The auditory 

 capsule, which contains the organ of hearing, has undergone the 

 most complete ossification, the bones present in it forming the 



