160 DR. R. BROOM ON 



it, is more primitive than the Polyprotoclont marsupials which 

 have lost it. It is very well developed in the Rodent, Lepus. 

 In Macroscelides it is only slightly developed in the young 

 specimens which I examined, but may be better developed in 

 the adult. 



Fig. 8 shows a section near the posterior end of the organ. 

 The organ is still seen to be of large size, lying in the U-shaped 

 cartilage which it nearly fills. Jacobson's cartilage rests on the 

 palatine plate of the maxillary, and is supported internally and 

 superiorly by the vomer. 



If the figures here given of sections of the snout of Tupaia be 

 compared with those I have given of sections of Macroscelides, 

 it will be seen that the two are formed on exactly the same type, 

 and that the differences are not greater than are seen in the 

 different families of the Diprotodont marsupials or of the Artio- 

 dactyles. Both genera agree closely with the Polyprotodont 

 marsupials, and, as will be seen from the study of the snout of 

 Gymnura, differ in almost eA^ery feature from that typical 

 Insectivore. 



The Organ of Jacobson in Gymnura. 

 (Plate II.) 



The specimen which I have examined is a very young animal, 

 probably recently born and about one fourth adult size. From the 

 snout to the base of the tail measures 90 mm. Except for a few 

 small vibrissa? on the snout it is entirely hairless. 



The nostrils are nearly terminal, but open laterally, and are 

 completely protected in front by the front of the nasal cartilage. 



A section through the middle of the nostril shows a narrow 

 septum, with above a well-developed alinasal and below a large 

 anterior nasal-floor cartilage. The anterior end of the inferior 

 turbinal is cut across supported by a cartilage which is connected 

 with the outer edge of the alinasal. 



A section through the posterior border of the nostril shows 

 the anterior nasal-floor cartilage as an outer part forming the 

 floor of the nostril and an inner narrow piece attached to the base 

 of the septum. The turbinal is large and has a large cartilage 

 attached to the alinasal. The lacrimal duct is seen opening on 

 the inner side of the turbinal. 



A section a short distance behind the nostril is remarkable 

 for the rather abrupt thickening of the nasa,l septum and the 

 great reduction of the inferior turbinal. The anterior nasal- 

 floor cartilage is still attached to the base of the septum. The 

 alinasal cartilage does not pass down on the outer wall of the 

 nasal passage, and the cartilage, which in more anterior sections 

 protected this wall, is reduced to a small trough of cartilage along 

 the furrow between the small turbinal and the other nasal wall. 



A few sections further back a most remarkable condition 

 presents itself, as is shown in PL II. fig. 9. The broad nasal 

 septum splits up into a median part and two lateral splints. 



