I.] THE FROG. 13 



between the two nasal sacs, as a cartilaginous partition 

 {septum narium), from which are given off, dorsally and 

 ventrally, transverse alse of cartilage which furnish a roof 

 and a floor, respectively, to the nasal chambers. These 

 pass into one another where the chondro-cranium ends an- 

 teriorly and give rise to a truncated terminal face, the lateral 

 angles of which are produced outwards and forwards into 

 two flattened pros-nasal processes; these widen externally 

 and support the adjacent portions of the premaxillse and 

 maxillae. From the ventral face, just behind the truncated 

 anterior end of the chondro-cranium, spring two slender 

 cartilages, the rhinal processes. Each of these inclines to- 

 wards the middle line and ends against the middle of the 

 posterior face of the ascending process of the premaxilla 

 by a vertically elongated extremity. An oval nodule of 

 cartilage is attached to the posterior face of the above- 

 named process, and serves to connect it with the 

 rhinal process. On the dorsal face of the chondro-cranium, 

 just above the point of attachment of the rhinal processes, 

 the external nasal apertures are situated, and the outer and 

 posterior margins of each of these apertures are surrounded 

 and supported by a curious curved process of the cartilagi- 

 nous ala — the alinasal process. Where the sphenoidal and 

 the ethmoidal portions of the sphenethmoid meet, a stout, 

 transverse, partly osseous and partly cartilaginous bar is 

 given off, which is perforated at its origin by the canal for 

 the orbito-nasal nerve. It then narrows, but becoming 

 flattened from above downwards, rapidly widens again, and 

 its axe-head-like extremity abuts against the inner face of 

 the maxilla. The anterior angle of the axe-head is free; 

 the posterior angle is continued back into a slender carti- 

 laginous pterygoid rod which bifurcates posteriorly; this (the 

 suspensorium) furnishes the articulation for Meckel's carti- 



