THE LATERAL VENTRICLE. 123 



Inner wall Septum pellucidum. 



Outer wall Caudate nucleus. 



The posterior horn (cornu posterius, Figs. 35, 36, 38, 39, 40 

 and 41) is directed backward and downward in a curve concave 

 inward, from the ventricular center into the occipital lobe; and, 

 like the occipital lobe, it first makes its appearance in the fifth 

 month of embryonic life. Its extremity bends medially toward 

 the posterior calcarine fissure, with which the horn is parallel. 

 The anterior calcarine fissure produces the ridge along the inner 

 wall called the calcar avis. The posterior horn is roofed over 

 by fibers from the splenium of the corpus callosum, which turn 

 down outside the horn and also form part of the external boundary. 

 In the external wall and in the roof and floor is also the optic 

 radiation. A well-marked bundle of fibers from the splenium, 

 forceps major, is found passing along the medial border of the roof 

 into the occipital lobe. It produces an eminence above the calcar 

 avis, called the bulb. The anterior extremity of the posterior horn 

 is continuous, inf eriorly, with the beginning of the inferior horn. At 

 the junction of the two is a triangular area, the trigonum collateral. 



The inferior horn (cornu inferius, Figs. 32, 38, 39 and 41) 

 is the ventricle of the temporal lobe. Its course is crescentic, 

 as it follows the perimeter of the internal capsule. It first runs 

 outward and backward from the body of the ventricle, then it 

 turns downward, and finally it proceeds horizontally forward 

 and inward to within an inch of the pole of the temporal lobe. 

 In horizontal section just below the general cavity of the ventricle, 

 the inferior horn is triangular. In that position it has a posterior 

 wall (or floor in the horizontal part), a medial wall, and a curved 

 antero-lateral wall (or roof in the horizontal portion) which is 

 continuous above with the outer wall and floor of the central 

 part of the ventricle. 



The parts found in the walls of the inferior horn may be enumer- 

 ated as follows: 



Roof (or antero-lateral wall) 



Inferior lamina of internal capsule, partially covered by 

 tail of caudate nucleus, stria terminalis and amygdala. 



Tapetum Floor (or posterior wall) 



