88 Proceedings of the Royal Society of Victoria. 



layers of the lateral wall, there being no inturning of the 

 capsule. In the Rabbit' and ]\Iarsupials, however, there is a 

 similar somewhat kidney-shape in the central portion of the 

 Organ, due only to sul)epithelial and glandular thickening. This 

 indentation, moreover, is not constant, as, occasionally, as above 

 stated, while one side i-etains more or less of the concavity in 

 its lateral wall, the Organ of the other side may be quite oval or 

 even circular in transverse outline. 



In vertical diameter the Organ varies from .32 to .6 mm. 

 Horizontal diameter, .12 to .28, very slightly less than in the 

 Rabbit, and slightly under half of that of the Dog and Guinea- 

 pig. Into the upper and lower sulci of the Organ there open a 

 considerable number of ducts from the gland mass on either side 

 of the nasal septun). Seven or eight of such ducts may at times 

 be seen in one single longitudinal section opening into the upper 

 or dorsal sulcus, and a lesser number into the ventral sulcus. 

 These ducts, which are short, wide, and have darkly staining walls, 

 lie at right angles to those from the same gland mass, which run 

 forwards longitudinally, and more or less parallel, till they open 

 into the vestibule close to the external orifice. The latter 

 longitudinal ducts are usually fifteen to twenty in number on 

 each side of the cartilaginous septum. 



Blood Vessels. 



Jacobson's Organ is well supplied with these (Figs. 5 and 6, 

 f., a., ct.^. Alongside its lateral wall, there run an artery and 

 two veins, the former curving round anteriorly, from dorsal to 

 ventral surfaces, and between the front end of the Organ and its 

 supporting cartilage in this region, while both laterally and 

 ventrally in the median wall is to be found a more or less 

 extensive plexus of blood vessels (Figs. 5, 6, c.t.). 



Nerves. 



In longitudinal sections, especially, there is to be noted a large 

 branch of the olfactory nerve passing forward horizontally and 

 entering into relation with the dorsal and mesial surfaces of the 



1 Q.J.M.S., vol. xxi., p. 558. 



