10 RELATIONS OF THE ORfiAN OF JACOBSON IN THE HORSE, 



satisfactory, as the present series sufficiently elucidates the natui-e 

 of the peculiarity, I think it well to publish the present results. 



The Horse differs from most mammals in having the jDremaxil- 

 laries developed in such a way as to carry the palate forward in 

 advance of the nares and forming a sort of rostrum — a condition 

 seen in a much greater degree in the Tapir. As a result of this 

 development a large j)ortion of the anterior part of the nasal 

 septum is clasped between the premaxillaries, and the lateral 

 cartilages, which in most mammals become the " cartilages of the 

 nasal floor," are here confined by the premaxillaries and prevented 

 from developing latei-ally to any great degree, and seem to com- 

 pensate for the want of lateral expansion by developing down- 

 wards. 



Figure 1, Plate i., I'epresents a section immediately behind the 

 point where the premaxillary gives off its palatine process. A 

 portion of the lateral cartilage (I.e.) is seen passing downwards 

 from the nasal septum (n.s.) between the premaxillary and the 

 palatine process. A little below it may be observed an oval 

 cartilage cut across— this is an anterior process from the lateral 

 cartilage. It passes well forward, approaching nearer to the 

 palate, and ending a little behind the rudimentary papilla. The 

 most noteworthy peculiarity of this section is that there is no 

 trace of the naso-palatine canal to be seen, nor is there in any 

 anterior section. Even by the sides of the papilla, where the 

 anterior opening of the canal would be expected, I have failed to 

 find even a rudiment. 



A little distance behind the plane of figure 1 the anterior 

 process of the latei'al cartilage is seen united with the main part, 

 which though still attached to the nasal septum is becoming 

 constricted off. In a slight concavity on the inferior end of the 

 cartilage is found on this plane the anterior closed end of the 

 imperfect naso-palatine canal (ii.p.c.). 



In figure 3 the naso-palatine canal is found to have a distinct 

 lumen, and on its inner side it is supported by a small downward 

 cartilaginous process. 



