144 PHYSIOLOGICAL SERIES. 



form of that of Tachyglossus (vide infra). The only marked 

 difference, and that of no systematic significance, is the 

 projection of the floccular lobes [which are lacking in this 

 r-peeimen]: in the Spiny Anteater's brain they are flattened 

 and sessile. 



In the separated cerebral hemisphere (fig. 36) part of the 

 overhanging neopallium has been removed in order to 

 expose the fascia dentata lying in the mesial wall of the 

 hemisphere. 



The peculiar position of this specialised fringe of the 

 hippocampus and its relations to the commissures agree 

 with the condition seen to much better advantage in the 

 specimen of the Spiny Anteater's hemisphere (D. 191). In 

 the Platypus, however, the caudo-ventral part of the hippo- 

 campal arc dwindles to much more insignificant proportions 

 than is the case in Tacliyglossus. 



It thus happens that that (caudo-ventral) part of the arc-, 

 which alone persists in an undisturbed condition in the 

 Eutherian brain, is here an exceedingly diminutive fciil- 

 like appendage of the chief mass of the hippocampus, which 

 is placed further forward in the hemisphere on the dorsal 

 aspect of the commissures. It is, moreover, a very signi- 

 ficant fact that this, the most bulky part of the hippo- 

 campus in the Monotreme, occupies this cephalic (anterior) 

 position in the mesial wall, which its representative in the 

 Sauropsida and many Ichthyopsida occupies. 



Presented by Prof. G. Elliot Smith. 



Elliot Smith, Jour. Anat. & Phys., vol.xxxiii. 1899, p. 310. 



D. 190. A cast of the cranial cavity of a Duck-billed Platypus 

 (OrnitJiorhynchus anatinus). 



This shows the actual size and shape (when viewed from 

 the dorsal aspect) of the brain o Platypus. The configu- 

 ration of the base of the brain cannot be accurate!} 

 because the casts of the huge maxillary parts of the tri- 

 geininal nerve are superposed. The most prominent part 

 of the mesial ridge between these nerves indicates the BUM 

 and shape of the pituitary body. 



Gervais, Nouv. Arch. Mus., t. v. 1869, p. 248. 



