1396-97.] Dr E. Broom on Mammalian Organ of Jacobson. 391 
A Contribution to the Comparative Anatomy of the 
Mammalian Organ of Jacobson. By R. Broom, M.D., 
B.Sc. Communicated by Sir William Turner. 
(Read June 7, 1897. ) 
{Abstract.) 
In this paper the author confines his attention to the relations of 
the organ, and especially to the structure of Jacobson’s cartilage, 
the nasal floor cartilage, and the different developments to which 
they give rise. From the study of a large series of forms he has 
been led to the following general conclusions: — (1) That the 
organ is generally well developed in the primitive groups, and 
feebly developed in the higher forms ; (2) that among allied 
animals the organ is, as a rule, better developed in the small 
species than in the large ; (3) that in the various members of each 
Natural Order the organ is constructed on a common type, which 
admits of only very slight variation ; and (4) that, even when the 
organ is quite absent in certain members of an Order, the nasal 
floor cartilages are constructed on the same type as in those 
members in which the organ is developed. 
From the very slight tendency there is in the organ and its 
cartilaginous adjuncts to vary with changing habits, the author 
concludes that the anatomy of the region affords a valuable factor 
in classification. A study has been made in most of the Mammalian 
orders, and the relationships and inter-affinities of the different 
types have been critically examined. 
In the Monotremata the organ is very well developed. The 
simple nasal floor cartilage in front gives rise behind to Jacobson’s 
cartilage and a well-developed outer nasal floor cartilage, which 
latter passes inwards and supports Jacobson’s cartilage. In this 
order Jacobson’s cartilage differs from all other mammals, and 
resembles lizards in forming a well-marked turbinal process. 
In the Marsupialia and Edentata the organ is much less de- 
