H2 ZOOTOMY. 



64. The epipterygoid (e.pt.) (so-called columella), a 

 slender rod of bone, lying just in front of and external to 

 the anterior edge of the prootic : below it articulates with 

 the pterygoid, above with the prootic. 



65. The columella auris (Fig. 36), a small rod of 

 combined bone and cartilage, lying in the dorsal wall of the 

 tympanic recess : its inner end is inserted into the fenestra 

 ovalis, a small aperture between the prootic and opisthotic, 

 while its outer end is, in the entire head, fixed to the inner 

 surface of the tympanic membrane. 



gt- 



FIG. 36. Lacerta agilis. The columella auris (after W. K. Parker) 

 x 14. The cartilaginous parts are dotted. 



e.st, extra- stapedial : i.st, infra-stapedial : m.st, medio-stapedial: 

 s.st, supra-stapedial : st. stapes. 



The columella auris consists of the following distinct parts which 

 are only to be made out by careful dissection of an entire head : (a) the 

 stapes, (st}, a small cartilaginous nodule in the fenestra ovalis : (b) the 

 medio-stapedial (nt.sf}, a bony bar connected with the stapes, the 

 ossification from it extending into the latter : (c) a cartilaginous rod 

 continuous with the distal end of the medio-stapedial, sending off a 

 downwardly directed process, the infra-stapedial (t.rf),-and expanding 

 at its outer or free extremity into a bar set transversely to the rest of the 

 columella like the head of a hammer : the lower somewhat pointed end 

 of this bar is the extra-stapedial (e.sf) : its dorsal extremity, the supra- 

 stapedial (s.st) is blunt and rounded, and gives off a process which 

 becomes connected with the auditory capsule. 



66. The vagus foramen (Fig. 35, IX, X, XI,), a small 

 aperture in the combined exoccipital and opisthotic, behind 



