24 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 57. 



they may represent in the reptilian skull, the same interpretation 

 must be given to them in Lemur, in which they sometimes occur in 

 the same position as in Ehynchocyon. 



Parker in his notable work on the morphology of the skull in the 

 Insectivora/ figures an embryo skull of Rhynchocyon cirnei, but the 

 stage apparently is too advanced to show the centers of ossification 

 of the lachrymal, which is represented as completely ossified without 

 any trace of sutures. From what I know of the ossification of the 

 lachrymal in the fetal skull of Twpaia I should say that it would 

 require a considerably yomiger stage to show whether there are one 

 or more centers in Rliynchocyon. It is not clear from his figures 

 whether there is a distinct postfrontal or not, but it would appear so 

 from the side view of the skull. In a like manner there seems to be 

 a large distinct prefrontal represented between the lachrymal and 

 frontal near the orbital margin, a fact which seems to strengthen the 

 evidence in favor of the view that the corresponding bone in the 

 adult skull, as described above, is a true homologue of the prefrontal. 

 If upon further investigation it is found that the lachrymal ossifies 

 from two centers, as it does in Twpaia, then one of these extra ele- 

 ments would have to be interpreted as a supraorbital. He does not 

 represent the zygomatic arch as divided into the three elements as 

 shown in the adult skull of RTiyncliocyon petersi above described, nor 

 does he say anything in the text about any of these bones. The lack 

 of information upon these important points is upon the whole rather 

 disappointing in a work of such magnitude. 



The homologies of the ossicles found in connection with the 

 lachrymal in the other genera of the Macroscelididae, notably those 

 of Cercodenus sultana and Petrodromus tetradaciylus, are less certain 

 of identification as reptilian elements. In view, however, of the 

 apparent complete absence of any other trace of a true jugal element 

 in some very young skulls of these species, it is not altogether 

 unlikely that the ossicle occurring at the junction of the lachrymal 

 with the remaining element of the zygoma may represent the 

 vestigial or reduced true jugal, which was originally larger and 

 occupied a more posterior position on the orbital rim, being now 

 represented by its anterior portion alone. In that event the prin- 

 cipal element in the jugal arch would be homologized as the cjuadrato- 

 jugal. In a like manner the upper ossicle attached to the lachrymal 

 may represent a prefrontal or supraorbital element which has been 

 crowded out, and has finally come to occupy a position on the edge 

 of the lachrymal. If this explanation be correct, it then follows that 

 all lachrymal crests, tubercles, protuberances, etc., so frequently 

 seen in the skulls of Marsupials, Insectivores, Rodents, and many 

 other groups, are to be interpreted in the same way and probably 



> Philos. Trans, Royal Soe. London, 1886, vol. 176, pi. 36. 



