SKULL AXD OTHEE BOXES OF LOXOMMA ALLMANNI. 221 



Loxomma presents all the characters of the order Labyrintho- 

 dontia of Owen, except " two occipital condyles" for articulation 

 with the atlas ; and it has, besides, other characters which also 

 show its affinity on the one hand with Fishes, and on the other 

 with Batrachians and the higher Reptiles. 



Its affinities with Pishes 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 vertebra. 

 ~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 vertebrae 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 articula- 

 tion 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, "Pa- 

 laeontology," 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 "exoccipitals 

 are immovably articulated in the cod below with the basioccipi- 

 tal, 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 movement upon the corres- 

 ponding anterior articular surfaces of the neurapophyses of the 

 atlas ; but we find no such articulations as these, that we arc 

 aware of, in Reptiles. The ossification of the parts here con- 

 cerned, 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 faci- 

 lity in turning its head, and that its movements in this respect 

 resembled rather those of Fishes than of Reptiles. 



By the possession of dcntigcrous 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 



