NOTE ON THE ORGAN OF JACOBSON 51 



tubes becomes much thickened, assuming all the characters of 

 olfactory epithelium. The outer layer of epithelium bends in / 

 towards the lumen of the tube, making the section of the organ ^ 

 assume a reniforra appearance, in the hilus of which may be 

 seen a large nerve embedded in glands. At this stage the mass 

 of cartilage is no longer visible. 



The organ of Jacobson, then, in the mouse has no connection 

 with the Stenonian canal. It is simply a tubular recess from the 

 nostril, situated in the septum. There is, moreover, no sur- 

 rounding cartilage. 



In the cat and hedgehog the case is quite different. In these 

 animals there is a direct communication between the organ iu 

 question at its anterior extremity and the Stenonian canal, where 

 this latter tube enters the nostril. 



IL The Cat. — My observations were made on the heads of 

 three kittens, taken from the uterus of a cat apparently about 

 three days before full time. 



In a vertical section at the spot where the Stenonian canal 

 enters the mouth the thickness of the bone (containing the 

 lateral incisor teeth) is considerable. The epithelium on the 

 floor of the nostril is of the compound scaly variety, as in the 

 mouse. The canal in this position is seen passing upwards and 

 outwards, being overhung by a horseshoe of hyaline cartilage. 

 In a section a little further back, the canal is seen bending ver- 

 tically upwards, and the cartilage becomes situated on its inner 

 side. In its passage upwards to the nostril the canal passes but 

 very slightly backwards, and hence vertical sections cut it in 

 considerable length. From the inner side of such a section of 

 the canal a diverticulum is seen passing inwards, which is received 

 into a concavity in the cartilage. This diverticulum is the 

 commencement of the organ of Jacobson. The Stenonian canal 

 opens into the anterior angle of a deep vertical chink, into 

 which the floor of the nostril is narrowed in front. The anterior 

 boundary of this chink is almost a vertical line, and is formed 

 by the thick mass of bone containing the incisor teeth. In a 

 section where the canal enters the nostril this might be taken 

 for a continuation of the canal. But that such is not the case 

 is proved in the section itself by the fact that the outer surface 

 of the chink is covered by cylindrical epithelium, and in sub- 

 sequent sections by their showing the change in level that has 

 taken place in the upper surface of the palate. The section of 

 the organ of Jacobson is now seen in the side of the septum, 

 and this change has taken place without its distance from the 

 under surface of the palate having become materially changed, 

 and hence it is caused by the sudden deepening of the nostril, and 

 not by any marked upward direction of its own tube. At teh 



