Osteology of Loxomma Allmanni. 59 



Its affinities with Fishes are evidenced by the presence of 

 the following characters : — 



By the existence of one concave articular surface, instead of 

 a condyle or condyles, on the posterior face of the basioccipital 

 bone, for articulation with the body of the first cervical ver- 

 tebra. No atlas has been discovered ; but it may be fairly 

 presumed that the anterior face of its centrum was concave, 

 since all the bodies of vertebras of Loxomma that have been 

 discovered are doubly concave, and the basioccipital itself is 

 also concave behind. 



By the existence of two facets on the exoccipitals for articu- 

 lation with the neural arch of the atlas. 



The former of these characters is almost altogether piscine ; 

 it occurs, however, only in Rana among Batrachians (Owen, 

 ' Palgeontolog.' p. 208), and is therefore rarely reptilian. The 

 second appears to be exclusively piscine ; for Prof. Owen 

 (Lect. on Comp. Anat. vol. ii. p. 91) says that the " ex-, 

 occipitals are immovably articulated in the cod below with the 

 basioccipital, behind with the neurapophyses of the atlas," 

 also that "in a few fishes (e. g. Fistularia) the exoccipitals 

 send back articular processes modified to allow a slight move- 

 ment upon the corresponding anterior articular surfaces of the 

 neurapophyses of the atlas ;" but we find no such articulations 

 as these, that we are aware of, in Reptiles. The ossification 

 of the parts here concerned, however, is less perfect in Fishes 

 than in Loxomma. 



It seems certain that the mode of articulation of the head to 

 the spinal column has been of such a nature as to allow of only 

 a very limited amount of motion, that Loxomma had little 

 facility in turning its head, and that its movements in this 

 respect resembled rather those of Fishes than of Reptiles. 



By the possession of dentigerous vomerine plates on the 

 palate. Lepidosteus and the Batrachia have these ; but we 

 also see that " in some alligators (All. niger) the divided 

 vomer extends far forward, expands anteriorly, and appears 

 upon the bony palate" (Owen, 'Anat, of Vertebr.' vol. i. 

 pp. 138 & 146), though it has no teeth. 



By the teeth being anchylosed to the bottom of their alveoli, 

 the base of the tooth blending gradually into the bony structure 

 around. This, however, is a reptilian as well as a piscine 

 character. The same may be said of the inequality in height 

 of the outer and inner alveolar borders of the mandible and, to 

 a less degree, of the maxilla also. In Loxomma the inner 

 border of the mandibular alveolus is very deficient, leaving 

 the teeth as it were agglutinated to and supported by the 

 external border only, which stands well up. This character 



