The Columella Aiiris in Amphibia. 599 



The fenestral plate is fused throughout its entire cephalic margin 

 with the ear capsule. This fusion is much greater in extent, rela- 

 tively, than in either Typhlomolge or the Plethodontidse. 



The ceratohyal is much produced caudally, its falcate distal por- 

 tion extending beyond the otic region. A short distance before the 

 caudal extremity is reached there arises from the dorsal edge a broad, 

 and strong ligament extending forwards for insertion upon the 

 fenestral plate (PI. X, Fig. 72). The stilus projects directly into 

 this just cephalad of which there arises another, the hyo-suspensorial 

 ligament, which passes cephalad for insertion upon the palatoquad- 

 rate. These ligaments are considered by Cope as one, namely, a 

 hyo-suspensorial ligament extending from the quadrate across the 

 ear capsule to the exoccipital. Parker treats them as two separate 

 and distinct ligaments. That portion extending to the quadrate he 

 calls the hyo-suspensorial while to the columellar portion he applies 

 the name suspensorio-stapedial. Functionally they are probably to 

 be considered as distinct, but in serial sections they appear to be 

 thickenings of the same sheet of fascia. 



The short and free stilus projecting into the ligamentum hyo- 

 columellare is more comprehensible in the light of the segmented 

 condition of this structure in Typhlomolge. Thus in Siren all sus- 

 pensorial communication of the fenestral plate with the exterior, 

 such as is found in other forms, is cut off. But it will be noted that 

 the ligamentum hyo-columellare in this form is strongly developed 

 which together with its firm attachment to the fenestral plate may 

 compensate for the absence of the usual skeletal connections. The 

 relation of the stilus to the facial nerve and blood vessels is that 

 found in the majority of forms. 



^ Three figures (PI. IX) illustrate the relations of the columella, 

 stilus and hyo-columellar ligament. In Fig. 61 the short stilus 

 is shown projecting out into the dense ligament, the diminutive plate 

 joined to the margin of the fenestra by connective tissue. Fig. 

 62 is through the caudal end of the columella of the opposite side. 

 In Fig. 63 the section is through the perilymphatic prominence, 

 a, caudo-lateral extension of the ear capsule. Slightly farther for- 

 wards the cartilage is hollowed out by a small recessus. The fenestra 



