H2 THE SKULL [CHAP. 



end of the auditory bulla. Immediately behind the bulla, 

 and to the outer side of the abutment of the paroccipital 

 process against it, is an oval hole (sm), partially divided by 

 a constriction into an inner and an outer division. In 

 the inner division the end of a small cylindrical plug of 

 bone, the tympanohyal, can generally be seen. The outer 

 division is the stylomastoid foramen, through which the 

 seventh nerve, or portio dura, makes its exit. The bone 

 forming its outer boundary is the mastoid portion of the 

 periotic. 



Connected with the posterior lateral parts of the cranium 

 are two appended bony parts : the lower jaw or mandible, 

 and the hyoidean apparatus. The former forms the frame- 

 work for the floor of the mouth, and supports the lower 

 series of teeth ; the latter gives a firm yet movable point 

 of attachment to the root of the tongue and to the larynx, 

 or organ of voice. 



The mandible consists of two symmetrical elongated rami 

 (see Fig. 46, p. 117), diverging behind, and coming in contact 

 in front at the middle line, by a roughened surface called the 

 symphysis (s] ; here they are firmly held together by inter- 

 posed fibrous tissue, or in old animals they may become 

 ankylosed. 



Each ramus is compressed from side to side, has a 

 thickened rounded lower border, slightly curved in the 

 longitudinal direction, and a nearly straight upper alveolar 

 border, in which the teeth are implanted. The inferior 

 border inclines upwards in front to meet the alveolar border 

 at the front of the symphysis. Near the posterior extremity 

 is the condyle (cd], a transversely-extended projection, with its 

 upper surface rounded in the antero-posterior direction, and 

 which, fitting into the glenoid cavity of the squamosal bone, 

 forms the hinge-like synovial articulation by which the lower 



