No. I.] SKELETAL ANATOMY OF AMPHIUMA. 27 



premaxillary, as has been shown in the case of the larva. Below 

 the premaxillary is found the unpaired piece of cartilage which 

 has already been referred to. There is no cartilaginous con- 

 nection between it and the processes from the nasal cartilages 

 ending in the angle between the body and the alveolar processes 

 of the premaxillary. Hence, my theory of the origin of the 

 unpaired cartilage is not demonstrated by the specimen in hand. 

 However, it is not disproved ; while the apparently transitional 

 character of the intervening tissues is favorable to the opinion 

 that the cartilage has but recently undergone conversion into 

 connective tissue. It is greatly to be desired that a specimen 

 of this species may soon be obtained of intermediate ao-e, so 

 that the origin of this structure may be definitely determined. 



The premaxillary has the same features as that of the adult. 

 I can, however, see no grounds for accepting Dr. Wiedersheim's 

 view as to the origin of the median descending plate and the 

 palatine process from the interseptal cartilage. There is no- 

 where to be seen such a transition from bone to unossified car- 

 tilage as might be expected, were the bone derived from the 

 cartilage. The relations between these portions of the premax- 

 illary are no more intimate than is that between these cartilages 

 and the descending processes of the frontals. There is thus no 

 sphenoidal ossification in this animal. 



It appears to me that many of the peculiar structures of the 

 Amphuima may be explained by considering its habits. It is 

 eminently a burrowing animal, as has been shown by many 

 observers. Such a mode of life would require and, in time, lead 

 to the production, probably, of a narrow and pointed snout, 

 instead of the rounded snout, so common among the Urodeles. 

 The ability to thrust the body rapidly into the earth at the 

 bottoms of rivers and swamps would also call for a solidly con- 

 structed cranium ; and accordingly, we find the skull of the 

 Amphiuma as thoroughly ossified as in the higher members of 

 its order. In the act of burrowing the premaxillary would be 

 especially exposed to pressure, and it would be essential that 

 this pressure should be transmitted to and sustained by the 

 other bones of the skull. This result is secured in a beautiful 

 and effective manner through the structure and connections of 

 the premaxillary. Its solidity is, first of all, secured by its 

 being composed of but a single piece. At the sides its alveolar 



