PAPERS ON BIOLOGY AND AGRICULTURE 131 



capsule have been made; also drawings of the nasal or- 

 gans, showing the relation of the organs to the capsule. 



The study of the nasal capsule was undertaken upon 

 the suggestion of Dr. G. M. Higgins, to whom the writer 

 is indebted greatly, not only for the supervision and 

 helpful suggestions of the work and the preparation of 

 this paper, but also for the material used. 



In a single toad larva, 14mm. total length, which has 

 formed the basis of this study, a completely chondrified 

 nasal capsule has not yet developed. Several structures, 

 however, are already formed so that satisfactory com- 

 parisons may be made, not only with the older stages 

 previously described, but with the capsules of corres- 

 ponding stages of Eana. 



The eavum cranii (CC), the cavity containing the 

 brain, is only partially formed, so that the nasal cavity is 

 practically continuous with that of the brain. The floor 

 of the brain case in its anterior part is formed by a rather 

 thick cartilage plate, the planum basale (PB), which is 

 continuous laterally with the lower margin of the alis- 

 phenoid cartilages (ALC). 



From the median line of the planum basale, just ante- 

 rior to the telencephalon, a small cylindrical process ex- 

 tends dorsally (Fig. 2) a short distance, to end in the 

 mesenchymatous tissue above. This is the beginning of 

 the posterior wall of the nasal capsule, and is ultimately 

 to separate the nasal cavity from the cavum cranii. It is 

 quite evident that this process, the ethmoidal column 

 (EC), is the first appearance of that structure later 

 known as the pons ethmoidalis, which connects the dorsal 

 margin of the alisphenoids just anterior to the brain. 



Anterior to the ethmoidal column, the planum basale 

 continues into that cartilage plate which forms the Pla- 

 num ethmoidalis (PE, Fig. 1). This structure, more 

 narrow along its posterior part, gradually increases in its 

 lateral dimension and forms a trapezoid whose anterior 

 margin exceeds the length of the posterior by one third. 

 The medial and posterior portions of each nasal organ 

 rest lightly upon the corresponding lateral surfaces of 

 this planum (XOR, Fig. 5), but the larger part of the 

 organ lies above and lateral to it. This portion of the 



