1909.] OF JACOBSOX IX THE AXT-BEAR. 681 



Owing to the alDsence of Avell developed incisors the pre- 

 maxillary bone is feeble and the j)alatine papilla far forward. 

 The papilla is rather small and has no trace of a supporting 

 cartilage. The naso-palatine, which is unusually long and passes 

 for some distance nearly directly backwards, opens by the side of 

 the papilla. 



A transverse section through the plane of the papilla shows the 

 nasal cavity completely surrounded by cai'tilage, the nasal septum 

 below being continued into the nasal-floor cartilage and this 

 laterally into the alinasal. 



Fig. 3 on PI. LXXI. shows a section a little behind the papilla. 

 The nasal-floor cartilage is here seen still attached to the nasal 

 septum but distinctly specialised. The lower glandular ridge of 

 the septum ij.g.r.) is seen cut across. The premaxilla has not yet 

 given off its palatine process. The naso-palatine canal is seen 

 under the inner pai-t of the premaxilla. 



Fig. 4 is some distance behind fig. 3. The nasal-floor cartilage 

 is free at its outer edge from the alinasal, and the palatine process 

 is now seen distinct from the premaxilla. 



Fig. 5 is only a short distance behind fig. 4. The naso-palatine 

 canal is seen curving up to open into the organ of Jacobson, and 

 the nasal-floor cartilage is dividing into an inner and outer part. 

 The palatine process of the premaxilla is of large size. Above and 

 to the inner side is a small ossification which may be the remains 

 of the prevomer. It is, however, very closely connected with the 

 anterior end of the true vomer and may have no morphological 

 significance. The anterior end of the maxilla is seen between the 

 premaxilla and its palatine process. 



Fig. 1 is a section across the whole nasal cavity a very short 

 distance behind the plane of fig. 5. The premaxilla is seen to be 

 well developed. At the upper part of the section the anterior 

 part of the nasal is shown, both parts of the bifurcated end being 

 seen. The nasal septum is slender and the alinasal continued 

 i-ound the upper and outer part of the cavity. The inferior 

 turbinal is cut across near its anterior end. On the inner side 

 of the alinasal is a small plate of cartilage (r.u.t.) of doubtful 

 significance. It is not attached to any other cartilage and would 

 appear to be a rudimentary suiDerior turbinal. Near the middle of 

 the nasal septum is seen a well-developed upper glandular ridge 

 which runs along the septnm. The nasal-floor cartilage is now 

 seen in three portions, the middle one of Avhich is the outer bar of 

 Jacobson's cartilage. The anterior end of the organ is seen cut 

 across, and below it the naso-palatine canal passing on to the 

 nasal cavity. 



A little behind this plane the outer bar is seen uniting with the 

 base of the inner part of Jacobson's cartilage and giving rise to the 

 V-shaped section seen in fig. 6. 



Fig. 6 shows the condition much behind fig. 1, and near the 

 middle of the oi'gan. 



Fig. 2 is a more enlarged figure of the organ and its related 



