THE ORGAN OF JACOBSON. 159 



PL I. fig. 1 shows a transverse section passing through the 

 front of the premaxillary bone. Here the nasal-floor cartilage is 

 seen detached from, the septum, and forms not only the floor bat 

 the support for the inferior turbinal. The anterior part of the 

 outer cartilaginous wall is also seen cut across. 



Fig. 2 cuts through the first incisor and the anterior part of 

 the papilla of the palate. The nasal-floor cartilage is seen con- 

 nected with the cartilage of the lateral wall and forming the 

 cartilaginous support of the inferior turbinal. The great size of 

 the papilla is well seen. The appearance of the structures in 

 this section resembles considerably a similar section through the 

 snout of Dldelphys, and also somewhat a similar section through 

 the snout of Dasypus. 



Fig. 3 represents a section nearly 1 mm. behind that repre- 

 sented in fig. 2. The papilla is seen occupied by a large papillary 

 cartilage. The recurrent nasal-floor cartilage has the inner 

 portion enlarged where it is about to become Jacobson's cartilage. 

 The inferior turbinal is further, up on the lateral nasal wall. 

 This section resembles a corresponding section through the snouts 

 of any of the Polyprotodont marsupials. In the structure of the 

 nasal cartilages the resemblance is rather with Dasyurus and 

 Dldelphys ; in the great development of the papilla and its 

 cartilage the resemblance is more with Perameles. 



Figs. 4-6 l-epresent three sections close to each other, and only 

 a short distance behind that shown in fig. 3. They illustrate the 

 relations of the naso-palatine canal, and the opening of the organ 

 of Jacobson into the nasal cavity. The peculiar structure which 

 I have elsewhere called the outer bar of Jacobson's cai'tilage is 

 well seen. In fig. 4 it is attached to the upper part of Jacobson's 

 cartilage. In fig. 5 it is free, and in fig. 6 attached to the lower 

 portion of Jacobson's cartilage. The structures in these sections 

 are typically Polyprotodont marsupial and resemble those of 

 Perameles as much as those of Perameles do those of Dasyurus or 

 Dldelphys, and considerably more than do those of any known 

 Diprotodont marsupial. 



The outer bar of Jacobson's cartilage is believed to represent 

 the remains of the turbinal of Jacobson's organ in the Mono- 

 tremata. It is present in all marsupials, in Dasypus, Orycteropus, 

 Macroscelides, and some Rodents, but is unknown in any of the 

 higher mammals. 



Fig. 7 represents a section considerably further back than that 

 shown in fig. 6. Here Jacobson's organ is seen well developed, 

 with a single blood-vessel on its outer side and another on its 

 inner, exactly as in Perameles and Dldelphys. Jacobson's cartilage 

 has the usual shape, and is supported internally and below by the 

 palatine process of the premaxillary. Along the floor of the 

 nasal cavity is a distinct posterior nasal-floor cartilage. This is 

 the only structure in the snout that is not typically Poly- 

 protodont marsupial. As the structure is well developed in 

 Echidna, it is manifest that in this respect Tupaia. which retains 



' 12* 



