102 MR. F, E, BEDDARD ON THE [Feb. 7, 



•yv'ai'ds expands and curves backwards as in Cynognathus, the 

 evidence does not show. The zygapophyses of the two sides are 

 fairly close together, and the aiticidar surface of the post- 

 zygapophysis looks downwards and outwards. Below the post- 

 zygapophysis is a small but distinct anapophysis. The vertebra 

 bears a fairly close resemblance to the posterior dorsals or lumbars 

 of Cynognathus and Microgomphoclon, but the base of the transverse 

 process or rib is stronger in Diademodon. The mammalian 

 vertebra which most closely resembles it is perhaps the presacral 

 vertebra of Basyurus. If the transverse process of this vertebra 

 be proved to be autogenous as in Phascolomys, then the affinity with 

 Basyurus would be very manifest. The lumbar vertebrfe, like all 

 the other vertebras in the Monotremes, are so much specialised and 

 in some respects degenerate, that they are much less like those of 

 the Theriodonts than are even those of the higher Eutherians. 



EXPLANATION OF PLATE X. 



Fig. 1. Side view of left dentaiy of Dhidemodoti mastacits. Nat. size. Pm., pre- 

 molars ; III., molars. 



Fig. 2. Upper surfaces of the seven lower molars of the right side. Nat. size. 



Fig. 3. Inner view of left ilium. Nat. size. 



Fig. 4, Outer view of left ischium. Nat. size. 



Fig. 5. Inner view of left pubis. Nat. size. 



Fig. 6. liestoration of left side of pelvis of Diademodon. i iiat. size. II. Ilium. 

 Is. Ischium. P«. Pubis. 



Fig. 7. Back view of left femur. Nat. size. G.T. Great trochanter. S.T. Small 

 trochanter. 



Fig. 8. Upper view of lumbar vertebra of Diademodon. Nat. size. 



Fig. 9. Side view of lumbar vertebra of Diademodon. Nat. size. 



7. A Contribuiion to the Knowledge of the Arteries o£ the 

 Brain in the Clasj Aves. By Frank E. Beddard, M.A., 

 F.R.S., Prosector to the Society. 



[Received January 19, 1905.] 



(Text-figures 15-20.) 



The course of the arteries of the base of the brain in birds does 

 not appear to have been much studied. Dr. Gadow, in the section 

 of Bronn's ' Thierreichs ' devoted to birds, figures one brain from 

 the ventral surface — a figure copied from a memoir by ISTeugebaur * 

 on the vascular system generally in birds. I am not, however, 

 acquainted with any comparative sketch of the ceiebral arterial 

 system in these animals. I believe, therefore, that the following 

 observations, based upon the study of material skilfully injected 

 by my assistant, Mr. E. Ockenden, will be of some use as a con- 

 tribution to the subject. 



Struthio masaicus <^ .- — I shall give a detailed account of the 

 brain of the Ostrich, which will enable me to be more brief iii 



* Nov. Act. Acad. Lcop.-Car. x.xi. 184o, p. 517. 



