The Columella Auris in Amphibia. 611 



that the columella and its siispensorial connection is homologous 

 throughout the urodele group, and no valid reason is known why 

 the homology should not be extended to include the Anura as well. 

 Inasmuch as a study of the relations and development in that group 

 has not been made, the homology of columella and plectrum is not 

 presented wath the emphasis of personal investigation. 



Ligaments. The only muscle that is in the region of the head 

 involved in this study is the Musculus cephalo-dorso-mandibularis 

 (M. depressor mandihuli). It has its origin largely, and in some 

 of the forms entirely, from the squamosum, and inserts by means 

 of a longer or shorter tendon upon the retro-articular process of the 

 OS articulare. Beneath the muscle, between it and the ear capsule, 

 palatoquadrate, hyoid and mandible, is the space filled in with con- 

 nective tissue containing the nerves and blood-vessels. The tissue 

 next the muscle is denser and comes into intimate relation with the 

 squamosum, palatoquadrate, stilus columellse, ceratohyal, and man- 

 dible. (For illustration, see Figs. 43, 51, 55, 61.) 



This submuscular fascia appears to be the foundation, out of which, 

 by thickening of different portions three ligamentous structures may 

 be formed: — (a) Ligamentum hyo-suspensoriale (palato-quadrate), 

 (b) Ligamentum hyo-mandibulare, (c) Ligamentum hyo-columellare. 

 These may all be present in the same species, Aveakly or strongly de- 

 veloped. Of these the last two have long been recognized (Hux- 

 ley '74) and are in general well described ; the hyo-columellar liga- 

 ment, however, has not been as adequately considered and is of more 

 interest here because of its connection with the columella. It is 

 best developed in Siren (Fig. 61, 62, 63, PI. IX), but its presence 

 has been mentioned in the first part of this paper in Amphiuma, 

 Cryptobranchus, Gyrinophilus, Spelerpes, Desmognathus ; and seems 

 to be more or less well developed in the Plethodontidse generally. It 

 will be referred to subsequently in connection with the discussion 

 of the function of the urodelan apparatus. It was not recognized 

 in Ambystoma, Triton, Diemictylus or Salamandra. 



A ligamentum palatoquadrato-columellare corresponding- to Hux- 

 ley's suspensorio-stapedial ligament described by him in IsTecturus 

 it noticeably absent in that form as well as in other urodeles. 



