380 



PEOF. G. ELLIOT SMITH ON THE 



of the lateral ventricle, its medullary layer bein"- part of the vcutricular liuing- ; whereas 

 the posterior wall of the sulcus is far removed from the ventricle, and its medullary layer 

 is not free but is fused to the general medullary mass of the hemisphere. 



No part of the pallial lining of the retrocalcarine and paracalcarine sulci takes any 

 direct share in forming the walls of the lateral ventricle. 



If we next examine a similar section in the cerebral hemisphere of an Ape, such as 

 Cercopilhecits (fig. 51), essentially the same state of affairs is revealed. The posterior 

 wall of the calcarine sulcus is far removed from the ventricle and its medullary layer is 

 fused to the general medullary mass. 



As the result of the greater obliquity of the calcarine sulcus and of the smaller size 

 of the hippocamj)Us, a much larger area of the anterior (or lateral, as it has now become) 

 wall of the calcarine sulcus is exposed in the ventricle and forms the " calcar avis." 

 The only difference Ijetween the conditions in the Lemur and the Ape is a quantitative 

 and not a qualitative one. As the result of the larger dimensions of the neopalliiim, the 



Fig-.52. 



The left cerebral hemisphere of (a) Nycticelvs, (h) Microcdms, (c) Tarsina, and {iJ) Ihipalc, dissected 

 to show the hippocampus and the calcarine eminence (.<■) \not the true calcar in (/ and h']. 



hemisphere has extended further backward and has produced a posterior diverticidum 

 of the lateral ventricle, in the mesial wall of which the calcar is found. In the Lemur 

 the homologue of the calcar is also found, even though there is no posterior cornu of the 

 ventricle, but it fiices the alveus of the hij^pocampus, so that no bulging calcar can be 

 seen Avhen the ventricle is opened. 



If the lateral wall of the hemisphere be dissected away in the brain of a Lemur which 

 has been toughened in some preservative fluid, a line of cleaA'age readily extends 

 backward from the posterior angle of the ventricle between the dense medulla of the 

 calcarine cortex and the looser medullary matter in contact with it; in this way the 

 observer can readily be deceived into the belief that a jiosterior cornu exists and that 

 a rounded calcar (iig. 50, .;•) projects into it. The region .r, however, is not the 

 homologue of the true calcar, as a comjjarison of figs. 50 and 51 will at once show. 

 The appearance of the " calcar," so exposed in the brains of jS'i/cilcehtis, Jlicroccbiia, 



