382 PROFESSOR OWEN ON THE GENUS DINORNIS. 
backward from the cerebral divisions of the entocarotids (g). The basilar artery 
transmits or receives the branches from the vertebral arteries (i). A division of the 
macromyelon, defining a “ pons,” is not more definitely marked than in most other birds. 
The cerebellum (Pl. XLV. figs. 1 & 2, ¢) is of a subcompressed, subconical shape ; it 
gives 64 lines in vertical, 5 lines in transverse diameter, and 6 lines in antero-posterior 
extent at the base. A rudimentary appendage or prominence represents the side lobes: 
the superficies is multiplied by about fifteen transverse folds, averaging 14 line in depth; 
their grey and white matters are shown in the section (ib. fig. 6,¢). About seven of 
these folds are visible on the exposed surface of the cerebellum (figs. 1, 2,¢). A short 
fissural trace of the primitive cavity (ib. fig. 6, c!) communicates with the macromyelonal 
one, called ‘‘ fourth ventricle.” 
The distinctive peculiarity in the base view of the brain in Apteryx is the small 
relative size of the optic lobes (figs. 3 & 4,6). M. Dareste was struck with the pecu- 
liarity in the specimen of the brain of an Apterya in the Museum of Comparative 
Anatomy in the Garden of Plants. He speaks of the optic lobes as “a peine visible a 
Vextérieur”', and justly notices this confirmation by comparative anatomy of the 
relation of the optic lobes to vision, which relation MM. Flourens and Mayer had 
inferred from physiological experiment. 
The optic lobes, reduced as they are in Apteryx, adhere, however, to the ornithic type 
by the degree in which they have diverged laterally from each other in the course of 
the brain’s acquisition of its mature characters’; they are ovate and subdepressed. 
The optic thalami (ib. fig. 4,¢) form a larger and more definite tract than in other 
birds, and contribute in a greater degree to the ‘‘radix optica,”’ or chiasma. 
The cavity or ventricle of the small optic lobe is shown in the section (fig. 6, 5’), and 
in the base view (fig. 4, 0'), in which the macromyelon, removed by a transverse section 
through the back parts of the optic lobes (é 0’) and the “crura cerebri” (%), exposes 
the rudimental hippocampal enlargements (/) and the fissures (m) by which the artery 
of the ‘* choroid plexus” penetrates the lateral ventricle. 
The cerebral hemispheres (a, a’, figs. 1 & 2) are smooth: a feeble indent at the side 
of the base indicates the “Sylvian fissure,” which receives a branch of the cerebral 
entocarotid (fig. 3, 7); there is a more feeble indication of a mid longitudinal tract at 
the upper and hinder part of the hemisphere (fig. 2, a), and still more feeble indication 
of a transverse frontal depression marking off, as it were, an anterior lobe (ib. a’). The 
structure of the hemisphere adheres closely to the avian type. Each “crus” expands 
and commingles its white fibres with grey matter to form a large ganglion or “ corpus 
striatum” (fig. 5,7), from the outer side of which the neurine, chiefly of the white 
1 Annales des Sciences Naturelles, Zoologie, 1856. His notice of this specimen is as follows :—‘“ Le 
cerveau de l’Apteryx, tel que je l’ai entreyu au travers de ses membranes, m’a paru présenter des particu- 
larités intéressantes. Malheureusement je n’ai pu obtenir l’autorisation de le disséquer, ou méme seulement 
de le dépouiller de ses membranes.’—Tom. cit. p. 50. ? Anat. of Vertebrates, vol. ii. p. 119. 
