55] THE NA SA L ORG A N IN A MPIIIBIA —HIGGINS 55 



ially into a small superior prenasal process which extends ventrally and 

 medially from the capsule. The inferior prenasal process is considerably 

 longer than the superior; it arises from the planum basale just in front of 

 the choanal gap and extends forwards and downwards into the internasal 

 space (Fig. 78). Forming the floor of the c. medium, and extending back- 

 ward beneath and slightly lateral to the lamina externa is a conical process 

 considerably larger than that in Bufo; the possible remnant of the original 

 cornu trabeculae. 



Two small foramina pierce the solum anterius; the smaller and more 

 dorsal conducts the nasalis internus from the capsule, while the larger more 

 medial one is the fenestra naso-basalis, considerably smaller than that 

 described for Bufo. 



RANA VIRIDESCENS 



The nasal capsules of the Arcifera and the Firmisternia are essentially 

 alike, and, although I lack a series of stages showing the chondrification of 

 the nasal capsule in Rana, the work of Gaupp (1893) has made it possible 

 to compare the growth of the nasal capsule of the frog in connection with 

 my own two stages. 



In a larva 28 mm. long (entire length), in which the characteristic 

 Anuran chondrocranium is beginning to develop, the nasal capsule (Fig. 40) 

 consists of an elongate planum basale (pb), with the anterior extension of 

 the trabeculae to the labial cartilages. The muscularis process of the 

 quadrate {mpq) has fused with the lateral wall of the planum basale, and 

 just above the junction of the two a dorsal process has arisen from the 

 basale, which is to become the side wall of the capsule (Fig. 83). Gaupp 

 (1893) has referred to this cartilage as the "Ethmoidal-pfeiler," but it 

 differs from the ethmoidal column of Amblystoma in which chondrification 

 of this bar is independent of the planum basale. 



Medial processes from the dorsal margin of each columna ethmoidalis 

 fuse in the middle line and form a pons (pe), recalling this same structure 

 in Amblystoma and in Salamandjra (Fig. '84). In all three genera the 

 cavum cranii and the nasal cavity are continuous during a part of the 

 larval development by means of the fenestra ethmoidalis (fen eth) ventral 

 to the pons. Unlike Triton and Diemictylus however, chondrification 

 from the pons to the planum basale soon develops the ethmoidal wall which 

 separates these cavities. 



Upon a level with the pons ethmoidalis, and arising from the dorsal 

 part of the ethmoidal column, a small process extends laterally toward the 

 muscularis process of the quadrate. A small opening, which must be 

 regarded as the foramen orbito-nasalis for the nasalis internus nerve, 

 pierces this process near its base; and from this identification, it follows 

 that this process must contain parts of both planum tectale and processus 

 antorbitalis, the latter being beneath the foramen. The more dorsal posi- 



