COMPARATIVE ANATOMY OF THE MAMMALIAN ORGAN OF JACOBSON. 249 



side the canal is opening into the nasal cavity. From this section it will thus be seen 

 that Jacobson's duct opens into the naso-palatine canal just as the canal is opening into 

 the nasal cavity. In this it agrees with Miniopterus and the hedgehog, and also with 

 most Marsupials. In fig. 30 we have a section through the body of the organ, and 

 showing the normal relations of the organ, the cartilage, and the palatine process. 



Bos. — In the Ruminants the condition has long ago been carefully studied, and the 

 structure and relations of the cartilages, etc., were fully described by Balogh in 1860, 

 though his illustrations unfortunately are exceedingly diagrammatic. Of the ruminant 

 type I have examined two stages of foetal calf and a young goat, but the peculiarities of 

 the arrangements are perhaps best shown in the larger of the foetal calves — one about 

 six inches in length. As in the pig, the condition of parts closely agrees with that in 

 Miniopterus, so in the Ruminants we have an arrangement as closely corresponding with 

 that of the Carnivora. In the cat we have a long naso-palatine canal, and the duct of 

 Jacobson opening into the canal much in front of the union of the canal and the nasal 

 cavity. In the Ruminant a precisely similar condition is found ; but the agreement of 

 the cartilaginous structures is even more remarkable. Fig. 33 represents a section 

 through the anterior part of the naso-palatine canal, and even in this plane the duct of 

 Jacobson is already seen to be split off from the canal. The nasal floor cartilage is very 

 well developed, and still attached to the nasal septum. Around the naso-palatine canal 

 and Jacobson's duct is a curved plate of cartilage in which there is no difficulty in recog- 

 nising the two elements — the inner, which embraces Jacobson's duct, being the anterior 

 process of Jacobson's cartilage, the outer, the anterior process of the outer nasal floor 

 cartilage. Between these anterior cartilaginous processes and the nasal floor cartilage 

 lies the delicate palatine process of the premaxillary. In fig. 34 we find the nasal floor 

 cartilage almost united with the anterior process of Jacobson's cartilage, and farther out 

 the outer nasal floor cartilage separated from the inner is seen united with its anterior 

 process. Fig. 35 shows the appearances just anterior to the opening of the naso-palatine 

 canal into the nasal cavity. Jacobson's cartilage has now attained its normal form, and 

 has as its support on the inner side the premaxillary palatine process. The lower part 

 of the outer nasal floor cartilage again forms a sort of nasal floor, as is found in 

 Miniopterus, and in the rabbit. The close agreement between the condition of parts in 

 the calf with those in the cat will be well seen by comparing figures 33 and 35 with 25 

 and 27 respectively. 



Equus. — In the horse we have an aberrant modification of the Ungulate type brought 

 about probably by the great development of the premaxillaries. As I have elsewhere 

 described the peculiarity in detail, I will only here briefly mention the main features. 



In the horse the naso-palatine canal does not open into the mouth, but ends blindly 

 after passing forward for a short distance. The organ of Jacobson, which is normally 

 formed, opens into the canal which carries the secretion back into the nasal cavity. 

 In connection with the rudimentary canal and the well-developed premaxillaries, the 

 cartilages are modified considerably anteriorly. The nasal floor cartilage is much com- 



