560 B. F. Kingsbury and II. I). Eeed. 



inter transversarius capitis inferior of the frog, Gaiipp, '96) develop 

 into a fascicle of small fibers which becomes separated ofP from the 

 above mentioned muscle and gains the attachments to the developing 

 operculum and the suprascapula. Its opercular attachment is shown 

 in the models pictured in Figs. 23 and 24 (PI. I) and also in Fig. 

 37 (PI. IV) in which both attachments are shown. 



In accord with the statement of Hasse ('73), the facial nerve 

 is entirely below (in front of) the columellar-squamosal connection, 

 the descriptions of other authors who have given its relations being 

 therefore incorrect. In Fig. 22, the three branches of the hyoman- 

 dibular division, ramus mandibularis internus, ramus mandibularis 

 externus, and ramus jugularis, are shown. Joining the R. jugularis 

 is the R. communieans IX (not shown) which pursues a course 

 dorsad to the carotid artery to join the R. jugularis where it passes 

 under the ligament. 



In Ambystoma, therefore, there are two fenestral structures which 

 succeed one another at transformation. The first which appears in 

 the larva, is the columella, whose stilus connects with the squamosum 

 and whose fenestral plate becomes associated with the otic capsule 

 at its cephalic end. At transformation the columella becomes fused 

 with the ear capsule and a second fenestral plate, the Operculum, 

 is cut out. This second structure is caudal and medial to the first, 

 possesses no process (stilus), is not connected with the squamosum 

 or palatoquadrate, but is joined by means of the M. opercularis to 

 the pectoral girdle. 



The examination by earlier workers of the otic region in Ambys- 

 toma or Siredon, — which is to be regarded as a permanent larva of 

 an Ambystoma, — has not lacked suggestion of the interesting condi- 

 tion found in this form. In Siredon, in which the condition has 

 usually been examined, Hasse ('73), Friedcnreich and Gegenbaur 

 ('49), as well as Wiedersheim ('77), Parker ('77), and Retzius 

 ('81), described a well ossified "operculum" of conical form, the 

 base of the cone fitting into the fenestra, the apex of the cone pro- 

 longed into a bony process attached to the palatoquadrate cartilage 

 by ligament (Gaupp, '99, p. 1040). The plate that fits into the 

 window possesses, according to Retzius, a cartiUiginous border and 



