Literary Notices. Ixxi 



MORPHOLOGY. 

 The Organ of Jacobson in Mammals. ^ 



This study was undertaken in part, apparently, for the purpose of 

 clearing up the relations of the Hyrax to the Ungulates and Rodents, 

 by an examination of the organ of Jacobson, which has marked differ- 

 ences in these two types. An examination of the characters which it 

 presents in Hyrax, it was hoped, would clearly indicate the position of 

 this obscure form. This expectation was fully justified by finding that 

 both the grosser and finer structure of Jacobson's organ hnks this type 

 rather with the Ungulates. The specimen used could not be exactly 

 located as to species, but was a Namaqualand form closely allied to 

 Procavia capensis. This is to be added to the already long list of rare 

 types which Dr. Broom has studied with reference to the comparative 

 anatomy of the organ of Jacobson. This study appears to be the first 

 work done upon the organ in the hyracoidian Ungulates. In a previ- 

 ous paper the author has called attention to the two great types of the 

 higher Mammalia in respect of the structure of Jacobson's organ. 

 As his conclusions on this point are better stated there, though referred 

 to in the present paper, we quote from it. "In the Prototheria we 

 have an organ in a highly-developed condition, well supphed with 

 glandular tissue, and having a large vascular plexus along its outer 

 side. . . . The examination of the organ in the higher Eutheria 

 also reveals some striking relationships. As a rule, the organ itself is 

 more or less rudimentary, the plexus absent, and the glandular tissue 

 much reduced. In the cartilages, however, it has been seen that there 

 is almost invariably a peculiar and characteristic development by which 

 any higher Eutherian in which the organ is developed, and in the ma- 

 jority of those even in which it is absent, can be at once distinguished 

 from any of the lower mammals. In the complex development of the 

 nasal floor cartilage we have, apparently, a thoroughly reliable charac- 

 ter by which the higher Eutheria can be divided off from the lower 

 into a distinct group by themselves. For this group I would propose 

 the name Ccenorhinata, while for those Eutheria which have the prim- 

 itive arrangement of the cartilages of the nasal floor the distinguishing 

 name Arcluzorhinata might be given. In the former group would be 

 included the following orders : Primates, Carnivora, Insectivora, 

 Chiroptera, and Ungulata; in the latter, the Edentata, and probably 



' On the Organ of Jacobson in the Hyrax, by R. Broom, M. D., B. Sc. 

 One Plate. The Journal of Anatomy and Physiology, July, 1898, pp. 709-713. 



