Turner, Morpliology of tlw Avian Ih-ain. iii 



In hrematoxylin and in aluminium-sulphate cochineal prepa- 

 rations, each cell has a faintly stained spherical nucleus and 

 a densely stained nucleolus. In different avian brains the 

 dimensions of these cells vary. In the thrushes [Hylocichla 

 sivainsoni, Turdus migratoriJis^ Sialia sialis) these are 

 from twenty-one to twenty-four micro-millimetres long and 

 from seven to nine micro-millimetres broad. In addition to 

 these large cells, the nidulus is well supplied with Deiter's 

 corpuscles. 



Bellonci has called this body the corpus geniculatum.(') 

 Since in the human brain we find two geniculate bodies, 

 it is bvit just that some reason should be given for consider- 

 ing this nidulus the homologue of the corpus geniculatum 

 externum. Ranney('-) describes the geniculate bodies of the 

 human brain as follows: 



" In the extcrjial geniculate body the gray matter is 

 arranged in laminse, which present, in cross sections made 

 through its substance, a zigzag outline, as if the lamina; had 

 been crushed or folded together. The cells of this nidulus 

 are large, granular and pigmented. 



"The internal geniculate body is less intimately con- 

 nected with the optic lobes and the fibres of the optic tract, 

 as proved by the latest researches of Flechsig, Gudden and 

 Ganzer. Its gray matter is not arranged i?i the manner 

 peculiar to its companion^ although it is apparently traversed 

 by the optic tract connected with both the nates and testes 

 cerebri." 



Therefore, since the above described contorted stratifica- 

 tion is peculiar to the corpus geniculatum externum, and since 

 the nidulus under consideration possesses that structure, the 

 evidence that that nidulus is the homologue of the mamma- 

 lian corpus geniculatum externum seems conclusive. 



A large number of nerve fibres pass around the corpus 



1 " Ueber die centrale Endigung des nervus Opticus bei den Vertebraten." Von 

 Professor Josef liellonci in Bologna. Zeit. f. wiss. Zool., Bd. XLVli, s. 16, Fig. iii, cgt. 



2 Op. cit., i^. 214. 



