180 ANATOMY OF THE RABBIT 



the angle (angulus mandibiilae), or angular apophysis. The 

 elongated articular surface is borne at the end of a vertical, or 

 slightly oblique, condyloid process (processus condyloideus). The 

 nerve and vessels of the mandible enter at the mandibular foramen 

 (foramen mandibulare), the latter being situated on the medial 

 surface of the bone immediately behind the last cheek-tooth. 

 Terminal portions of the same structures emerge on the lateral sur- 

 face through the mental foramen, a little in front of the cheek teeth. 

 The mandible is described in greater detail starting on page 195. 



The Bones of the Skull 

 The Occipital Bone 



The occipital bone (os occipitale) is the first of the basicranial 

 segments as numbered from the occipital articulation forward. It 

 forms the posterior boundary of the skull and establishes the 

 connection of the latter with the vertebral column. Its external 

 surface is identifiable for the most part with the nuchal surface, 

 but a portion of it falls in the horizontal plane of the basis cranii. 

 The internal surface is partly exposed to the cranial cavity and 

 forms the posterior, dorsal, and ventral boundaries of the posterior 

 cranial fossa. The remaining portion is excluded from the cranial 

 cavity, being applied instead to the broad posterior surfaces of the 

 petrotympanic bones. 



The occipital bone is divisible into four portions, namely, the 

 basilar portion (pars basilaris) or basioccipital, the paired lateral 

 portions (partes laterales), or exoccipitals, and the squamous 

 portion (squama occipitalis), or supraoccipital. All four portions 

 take part in the formation of the foramen magnum. In the young 

 animal (Fig. 25) they are represented by separate elements, 

 formed in a continuous mass of cartilage, and united for a time by 

 synchondroses, but in the course of growth they become fused to 

 form a single occipital bone. 



The basioccipital is that portion lying below and in front of 

 the foramen magnum. Its main surfaces are respectively dorsal 

 and ventral. Its anterior margin is united with the posterior 

 margin of the basisphenoid by a thin, transverse cartilage union, 



