On the Skull of Tritylodon longaevus, &h}en. 283 



XXXI. — On the Skull o/Tiitylodon longrevus, Owen. 

 By Dr. Beanislav Petronievics. 



[Plate X.] 



Since Owen described in 1884, for the first time as mammalian, 

 the skull of the single specimen of Tritylodon existing in the 

 British Museum, several authors have re-examined his state- 

 ments. Seeley, in 1888, declared Tritylodon to be a 

 " bunotheroid Rodent " ; but in 1894, after his discovery 

 of Gomphodontia, he gave up this opinion and declared 

 Tritylodon a " theriodont Reptile " or as " intermediate 

 between Mammals and Theriodonts.^' R. Broom, in 1904, 

 showed that the reasons of Seeley for the statement that 

 Tritylodon was a reptile are not tenable. In 1910, after 

 having studied the specimen, Broom established the presence 

 of new sutures between bones which had been wholly over- 

 looked by the earlier observers, and so reinforced his opinion 

 that Tritylodon is a true mammalian. 



Having examined the specimen at the end of last year 

 while in London, I believe that some new sutures can be 

 made out, and that the limits between the bones are somewhat 

 different from those establisiied by Broom. A new prepara- 

 tion of the specimen has also cleared up some controversial 

 points. 



Text-fig. 1 shows the upper view of the skull. The 

 plainest suture is that separating on the left side for some 

 distance the nasal from the maxillary. In the front part of 

 this suture begins another, which is for the first time plainly 

 to be seen only with a magnifying-glass (it lies just above a 

 zig-zag crack). The prolongation of this latter suture on the 

 right is not clearly indicated, but is probable. If so, the whole 

 would separate the nasal from the frontal ; but it is not 

 impossible that the visible part separates the lacrimal from 

 the nasal. 



The sutures separating the prefrontal from the frontal and 

 lacrimal are doubtful or not at all indicated. The right side 

 is so damaged that only the suture bounding the maxillary is 

 to be seen for some distance. 



The septoraaxillaries, first observed by Broom, are now, 

 after the new preparation, plainly (comp. text-fig. 1 and the 

 photograph of the nares in Fl. X. fig. 1) to be seen. They 

 limit tlie nares laterally, cross them from below, and send a 

 short joint process above, which seems to meet in the middle 



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