515 



and his figures of the supposed stages in the transition approach very 

 closely to the condition in the model. 



The angular bone in the mammal being identified, the membrane 

 ossification below the malleo-meckelian bar must, of necessity, have 

 other homologies, and a consideration of the Cynodont jaw suggests 

 that it must be either pre-articular or surangular. Since it lies rather 

 more to the outside of Meckel than the inside it is probably suran- 

 gular. 



It is interesting that in the foetus with its jaw in the Cynodont 

 stage the masticatory muscles are all attached to the dentary in the 

 normal manner — a condition which Watson considered to be the 

 case in Cynodonts. 



I must express my thanks to Mr. Watson for suggestions which 

 have been adopted in this note, and for the figures of the Cyno- 

 dont jaw. 



BIBLIOGRAPHY. 



Broom, R., Observations on the development of the Marsupial skull. Proc. 



Linn. Soc. N. S. Wales, Vol. XXXIV, 1909, Part 2. 

 Bboom, R., The Structure of the Internal Ear and the Relations of the basi- 



cranial nerves in Dicynodon, and on the homologies of the Mammalian 



auditory ossicles. Proc. Zool. Soc. Lond., June 1912. 

 FtJCHS, H., Über die Beziehungen zwischen den Theromorphen Copy's bezw. 



den Therapsiden Broom's und den Säugetieren etc. Ztschr. f. Morph, u. 



Anthrop., Bd. XIV, pp. 367-438, 1911. 

 Gadow, H., On the modifications of the first and second visceral arches, with 



especial reference to the homologies of the auditory ossicles. Phil. Trans., 



Vol. 179, 1888. 

 KiNesLET, J. S., The ossicula auditus. Tufts College Studies, Vol. I, No. 6, 



1900. 

 Watson, D. M. S., On some Reptilian lower jaws. Ann. and Mag. Nat. Hist,, 



Series 8, Vol. X, Dec. 1912. 



33* 



