120 ILLINOIS STATE ACADEMY OF SCIENCE 



nal ears. On this interpretation, therefore, the optic 

 nerve to the right lateral eye is of the right encephalon ; 

 while that on the left, likewise belongs to the left encep 

 halon. 



The compound cerebrum is difficult of interpretation. 

 Its anterior is more nearly typical of the normal telen- 

 cephalon; but it is quite evident that the posterior por- 

 tions are parts of a fused unit. Although normal sulci 

 and gyri abound, yet identification of frontal, temporal 

 and occipital lobes as such is impossible (Fig. 7). 



THE SKELETON 



Correlated with the double cerebro-spinal axis, there 

 are two spinal columns, two sets of ribs and two sterna. 

 Each column is conspicuously twisted and curved; that 

 of the larger animal is the longer of the two and consists 

 of some forty vertebrae, while but twenty-six are present 

 in the smaller column. The terminal vertebra of the 

 latter is a mal-formation, and evidently is composed of 

 portions of the vertebrae in the posterior lumbar region 

 which have fused into a knob-like structure held between 

 the paired ilia of the greatly reduced pelvic girdle. The 

 numbers of vertebrae in the more anterior regions are 

 identical for both animals, there occurring, however, a 

 considerable reduction in the lumbar, sacral and caudal 

 regions of the smaller animal. 



The pelvic girdle is normal in the larger pig, but in the 

 smaller one it represents' the most posterior skeletal 

 structure in the trunk. It is a peculiar Y-shaped struc- 

 ture. The arms of the Y are represented by normal ilia 

 which support the end of the truncate spinal column; 

 while the median posterior part is formed by a fusion of 

 the two ischia and pubis bones. They are both greatly 

 reduced and are held together by heavy strands of fibrous 

 tissue. 



THE SKULL 



The skull is a fused structure. Its anterior half is nor- 

 mal; but the posterior half comprises corresponding 

 halves of adjacent skulls. Consequently, two occipitals 

 and four parietals are identified upon the dorsal surface, 



