12 RELATIONS OP THE ORGAN OF JACOBSOX IX THE HORSE, 



In almost all other respects there is a close agreement between 

 the condition of parts in the Horse and those in most other 

 Ungulates. 



Pig. 10 shows a section of part of the nose of a very small foetal 

 Calf. Here both Jacobson's and Stenson's cartilages are well 

 developed and seem distinct from the broad nasal-floor cartilage. 

 If this be compared with figures 4 or 5 the close resemblance will 

 be seen; in fact the only marked difference is that in the Horse 

 the cartilages of Jacobson and Stenson are united with the nasal- 

 floor cartilage, in the Calf distinct. But all the corresponding 

 parts can easily be observed. 



Figure 11 represents a section of the foetal Calf corresponding 

 to figure 6 in the Horse. Here the duct cartilages are united 

 with the nasal-floor cartilage as in the Horse. The resemblance 

 is, 'however, somewhat marred by the enormous de^'elopment of 

 the cartilage of the nasal wall in the Calf. Such variations in 

 cartilaginous development, however, occur in very nearly allied 

 forms as the Cat and Dog. 



The agreement of figure 12 with figure 8 is most striking. 



The peculiarities in the Horse are probably due to the strong 

 development of the premaxillary bones leading to the occlusion 

 of the anterior part of the naso-palatine canal and to the vertical 

 direction assumed by the lateral cartilage permitting the duct 

 cartilages to remain united with the main body. 



The similar condition in the Camel is probably accounted for 

 by the fact that its very recent ancestors had remarkably well 

 developed incisors, e.g , Protolabes from the Upper Miocene of 

 Oregon. 



In the Giraffe the explanation is not very manifest. 



I have to acknowledge my indebtedness to Dr. John Mackie 

 and Mr. A. Robb, F.R.C.V.S., of Glasgow, for the foetal horse 

 examined, and to Mr. Alf. Swan, of Taralga, for the icetal calf. 



