COMPOSITION OF BRAIN OF ATAXIC PIGEONS 91 



males of both ataxic groups have smaller brains (table 4) than 

 have the males of either normal group. The females of both 

 ataxic groups have smaller brains than the females of either 

 normal group. 



The cerebrum of all of the above-mentioned groups and subdi- 

 visions of groups of ataxics is smaller than the corresponding 

 groups of normals in a precisely similar way except that the fe- 

 males of the less ataxic group have a larger cerebrum than do the 

 females of the other three groups. The females of the strongly 

 ataxic group have the smallest cerebrum found for the four 

 groups. 



The cerebellum-medulla of all the ataxic groups and subdivisions 

 is smaller in every case. 



Further study of these data (four comparable age and strain 

 groups of table 4) shows, moreover, that the posterior portion 

 of the brain (cerebellum-medulla) of the ataxic groups is dispro- 

 portionately small in comparison with the cerebrum. That is 

 to say, the cerebrum of ataxics is somewhat reduced (1.5 per cent 

 in males and 0.0 per cent in females) below that of the normals, 

 while the cerebellum-medulla is much below (7.2 per cent in 

 males and 5.4 per cent in females) the normal size. The mean 

 weight of the cerebrum of the older ataxics is 1.3 per cent below 

 that of the older normals. That of the younger ataxics 1.7 per 

 cent below that of the younger normals. For the cerebellum- 

 medulla these figures are 5.3 and 5.5 per cent, respectively. The 

 disproportionate decrease of the ataxic cerebellum-medulla is 

 also shown by the figures for the 'ratio of parts' of the brain. 

 These figures are given in the next to the last column of table 4. 

 All of the (four) subdivisions of ataxics are there shown to have 

 abnormally small posterior brains. These same ratios also dem- 

 onstrate that in all of the four comparable groups — normals and 

 ataxics — the cerebellum-medulla is a smaller fraction of the total 

 brain in females than in males. 



It follows, therefore, that ataxia carries the male brain in the 

 direction of the normal female brain, both in regard to size and 

 relative proportion of its parts. We have hitherto noted that 

 ataxia also reduces the body size of the male; this is again in the 



