Palaeontology and Zoology. — '' Fhylogenetic and Ontogenetic 

 Increase of the . Volume of the Brain in Vertebrata" . By 

 Prof. EuG. Dubois. 



^Communicated at the meeting of June 24, 1922). 



One of the most striking and important palaeontological facts ever 

 brougiit to light ill the investigation of the strata of the earth, is 

 that of the extremely slight volume which the encephalon possesses 

 in the earliest forms of Reptiles, Birds and Mammals. By tliis 

 feature do these for the rest very differentiate(i and often gigantic 

 earliest representatives of their class ditfer from the forms immediately 

 following them and from the modern ones, in a way which must 

 almost seem ridiculous to the comparative anatomist. 



As regards Reptiles this has especially become known, by the 

 discoveries of Marsh, about the Dinosauria, the principal terrestrial 

 animals of the Mesozoic Era. In them the spinal canal, in its whole 

 length, was not seldom wider than the cranial cavity. In Stegosau- 

 rus, from the Lowest Cretaceous in Wyoming, the cross-section of 

 ^^he sacral enlargement of the spinal canal (this in connection with 

 the large hind-legs) was ten times as large as the cranial cavity. In 

 a Diplodocus of a computed body length of 24 meters, from the same 

 strata, this cavity is only 9 cm. long and 5 cm. wide, whereas that 

 of an adult alligator, with a tenth of that maximum body length of 

 its mesozoic distant relation, has a length of 67, (^ni. and a width 

 of 3 cm. Also in Theromorpha and Pterosauria the cranial cavity 

 is verj' small. 



Ichthyornis, described by Marsh from the Upper Cretaceous of 

 Kansas, possessed only the third of the cranial capacity of the Large 

 Sea Swallow (Sterna cantiaca), with which this toothed Mesozoic bird 

 bore considerable resemblance in size and structure of its skeleton, 

 probably also- the mode of life of the two birds was similar. 



In the class of the Mammalia, the Eocene primitive Carnivora, the 

 Creodontia, possessed very little encephalon, which appears clearly 

 on comparison of the cast of the brain-cavity of Arctocyon, from 

 the Basal Eocene of Reims, with that of a dog of similar size of 

 body (Fig. 1, A). The Condylarthra from the Lower Eocene, from 

 which the existing sub-orders, the Perissodactyla and Artiodactyla 



