62 THE ANATOMY OF VERTEBRATED ANIMALS. 



structm-e, and become the optic thalami. Its roof, on the 

 other hand, resembles that of the foui-th ventricle, in 

 remaining very thin, and, indeed, a mere membrane. The 

 pineal gland, or epiphysis cerebri, is developed in connection 

 with the upper wall of the third ventricle ; and, at the sides 

 of its roof, are two nei-vous bands, which iirn to the pineal 

 gland, and are called its peduncles. 



The front wall of the vesicle, in part, becomes the so-called 

 lamina terminalis, which is the delicate anterior boimdary 

 of the third ventricle. In certain directions, however, it 

 thickens and gives rise to thi-ee sets of fibres, one trans- 

 verse and two vertical — the former lying in front of the 

 latter. The transverse fibres pass on either side into the 

 corpora striata, and constitute the anterior commiss^ire which 

 connects those bodies. The vertical fibres are the anterior 

 pillars of the fornix, and they pass below into the floor of 

 the third ventricle, and into the corpora mammillaria, when 

 those structures are developed. 



The outer and imder waU of each cerebral hemisphere 

 thickens and becomes the corpus striatum, a ganglionic 

 sti-ucture which, from its origin, necessai-ily abuts against 

 the outer and anterior part of the optic thalamus. The 

 line of demarcation between the two corresponds with the 

 lower Kp (tarnia semicircidaris) of the aperture of commimi- 

 cation (called th.e fm-amen of Munro) between the third ven- 

 tricle and the cavity of the cerebral hemisphere, which is now 

 termed the lateral ventricle. In the higher Vertehrata, the 

 upper lip of the foramen of Munro thickens, and becomes 

 converted into a bundle of longitiidinal fibres, which is con- 

 tinuous, anteriorly, with the anterior pillars of the fornix 

 before mentioned. Posteriorly, these longitudinal fibres are 

 continued backwards and downwards along the inner wall 

 of the cerebral hemisphere, following the junction of the 

 corpora striata and optic thalami, and pass into a thicken- 

 ing of the wall of the hemisphere, which projects into the 

 lateral ventricle, and is called the hippocampus major. Thus 

 a longitudinal commissural band of nervous fibres, extend- 

 ing from the fioor of the third ventricle to that of the lateral 



