xxii Journal of Comparative Neurology. 



pulvinar and anterior quadrigemina. These latter fibres, however do 

 not seem to transmit visual impressions and a lesion there does not 

 seem to cause a defect in the visual field. From the ganglion cells of 

 the geniculate body fibres pass backward into the occipital optic tract. 

 They form a compact fasciculus about 5 mm. in diameter, which 

 passes at the level of the first temporal fissure and second temporal 

 convolution backwards to the bottom of the calcarine fissure. In this 

 optic path the fibres for the dorsal half of the retina lie dorsad, as in 

 the anterior part of the tract. The cortical visual centre lies at the 

 bottom of the calcarine fissure, and is restricted to it. A unilateral 

 lesion in this fissure causes complete hemianopsia. The pulvinar and 

 quadrigemina are also connected with the cortical visual centre; these 

 are probably reflex paths. The theory that the visual tract takes part 

 of the formation of the internal capsule or decussates behind the chi- 

 asm is incorrect. The macula is often innervated from both sides of 

 rhe brain. 



The Roof of the Diencephalon iii Petromyzon. 1 



In a brief paper, full of interesting suggestions, Professor Burck- 

 hardt indicates the inappropriateness of the term lobus olfactorius im- 

 par, as proposed by Kupffer, and substitutes recessus neuroporicus, 

 which should be at once adopted. 



The pineal stalk enters the lower pineal vesicle not the upper, as 

 supposed by Ahlborn. But the two communicate as indicated by the 

 latter author. Burckhardt finds the prepineal segment or " polster," 

 followed by the velum and paraphysis, as in other vertebrates. In 

 the later stages there is a retrogression rather than development in 

 these parts. From this and other recent communications it appears 

 that there is now no difficulty in applying homologies throughout the 

 vertebrate series. 



The Effect of Reflex and Central Irritation of the Optic Nerve upon the 

 Position of the Cones in the Retina. 



Nahmmacher has investigated the retina of the frog with the 

 view to determine whether contraction of the cones is produced by 

 the irritation of centrifugal fibres. It will be remembered that Grijns 

 has determined physiologically the existence of such centrifugal tracts 



Burckhardt, R. Die Homologien des Zwischenhirndaches und ihre Be- 

 deutung fur die Morphologie des Hirns bei niederen Vertebraten. Ariat. An- 

 seiger, IX, 5-6. 



