6& WILLIAM PATTEN. 



spheres (fig. 51), another, farther back (fig. 50), showing the 

 growth of the lobes over the rest of the brain. A third cerebral 

 lobe, the median internal lobe, or ^^ corpus striatum," is 

 now visible on the anterior inner face of each hemisphere 

 (fig. 51, c. s.). It is an oblong lobe_, extending about half the 

 length of the median face of the hemispheres. Even at a 

 much later period its thick cortical layer of cells is never 

 convoluted like the rest of the hemispheres, and it contains a 

 great medullary core, terminating blindly in front, and behind 

 in a great bundle of medullary substance that forms a part of 

 the cerebral peduncles (fig. 43, p. c. s.). By comparing figs. 

 47 — 49 a fair idea of the enormous increase in size of the 

 cerebral hemispheres may be obtained. These are all young 

 specimens, however ; the hemispheres are still larger in the 

 adult, as may be seen in fig. 53, a camera drawing of a section 

 through about the middle of the brain. The extraordinary 

 convolution of the cortical substance, formed of very small, 

 deeply stained nuclei, stands out in sharp contrast with the un- 

 stained medullary portions. One should observe the slender 

 peduncles of the hemisphere, the large space or vesicle (v.^), 

 sometimes filled with a mass of loose connective tissue, and 

 the now much-reduced semicircular lobes [s. /.). 



The semicircular lobes undergo strange modifications. 

 The two curved lobes seen in fig. 59 grow inward and back- 

 ward beneath the braiu till they cover its whole median hsemal 

 surface. They are seen in cross-section in fig. 27, and their 

 extent is dimly shown through the rest of the brain in figs. 24 

 and 25. They reach their greatest relative extent in the 

 second larval stage, as shown in fig. 46 s. I. Some time before 

 this there are split off from the median eye-tube two clear 

 nerve-strands, which now terminate in conical swellings on the 

 anterior ends of the semicircular lobes (fig. 46). The latter 

 are now joined with each other at their posterior ends, and no 

 longer show any trace of their dual origin. The lateral and 

 posterior margins of the semicircular lobes contain small, 

 densely crowded, and deeply stained nuclei, which are appa- 

 rently multiplying rapidly, and when the brain is stained and 



