680 DR. R. BROOM ON THE ORGAN [Juiie 15, 



marked groups of mammal-like reptiles, it has become necessary 

 to subdivide the group, forming either two new orders or two sub- 

 orders. The older group, which is confined to Permian beds, has 

 a single occipital condyle and a Rhynchocephalian palate, and has 

 been named Therocephalia. The other group, which is i^estricted 

 to Upper Triassic beds, has two occipital condyles and a mammal- 

 like secondary palate, and usually complex molars. This group 

 should retain Owen's original name Cynodontia. Doubtless the 

 later group is descended from the earlier, and Bauria, though a 

 Cynodont, to some extent foi-ms a connecting link. The 

 Cynodonts are of exceptional interest, as there is little doubt the 

 mammals have arisen from one of the members. 



The following papers were read : — 



1. On the Organ of Jacobson in Orycteropus. 

 By E. Broom, D.Sc, C.M.Z.S. 



[Received June 3, 1909.] 



(Plate LXXI.*) 



A-bout 1898, in studying the comparative anatomy of the organ 

 of Jacobson in Mammals, I observed that throughout whole groups 

 the structure and relations of the organ vaiied very little, and 

 that as the organ seemed to be less affected by change of habits 

 than almost any other, it was of great importance in revealing the 

 obscured affinities of aberrant forms. It was seen that, notwith- 

 standing the enormous differences in most points between the 

 Ungulates, the Carnivora, the Chiroptera, and the Insectivora, the 

 same type of organ is found in all, while a markedly different 

 type is found in all Rodents, and a third type in Dasypus. When 

 the aberrant Macroscelides was examined, it was found that the 

 organ was not at all like that of the noi-mal Insectivores but 

 almost typically Marsupial, showing that though for convenience 

 the Elephant-shrew is placed with the Insectivora it has probably 

 little real afiinity with them. 



Owing to the apjDarently isolated position occupied by Orycte- 

 ropus, as shown by its dentition and niunerous other characters, 

 I had long been anxious to examine its organ of Jacobson, but it 

 is only quite recently that I have had an opportunity of so doing, 

 when, through the kindness of Dr. Peringuey, of the South 

 African Museum, I obtained the head of a recently bom 

 specimen. 



The organ and its relations have been studied by means of 

 transverse sections, so that a comparison is easily made with the 

 large number of other mammals in which the organ has been 

 similarly studied. 



* For explanation of the Plate see p. 683. 



