368 CHARLES CLIFFORD MACKLIN 



The parietal plate (fig. 3) is a thin, semi-crescentic plate of 

 cartilage, situa.ted above and. behind the pars canalicularis of 

 the otic capsule, and bearing upon its median surface a concave 

 impression for the brain (fig. 5) . The ventral extremity is wide, 

 and is surmounted by an irregularly formed and rudimentary 

 portion, the upper border of which is overlaid laterally by the 

 caudal edge of the parietal bone. Above this part, and lying 

 in the membrane within the parietal bone is to be seen, on the 

 right side, an elongated nodule of cartilage, which may be known 

 as the cartilago cranii lateralis (fig. 3) — probably a remnant of 

 the side wall in this region. On the left side there is a somewhat 

 smaller nodule. That this portion is undergoing retrogression 

 is evident from a comprison with the models of Levi, on the one 

 hand, and with the model of Hertwig on the other, when it is 

 seen that the 14 nam. stage of Levi marks, perhaps, the stage of 

 greatest development of the parietal plate, there being, after this, 

 a progressive reduction, moderate in the 28 nam. stage of Levi 

 and in my model, and pronounced in that of Hertwig. 



With the otic capsule the parietal plate is connected at two 

 points — in front through the capsuloparietal commissure, and 

 below this through the bridge of cartilage between the capsulo- 

 parietal and capsulooccipital fissures. The ventral edge is 

 indented and presents no evidence of the ^heno-parietal com- 

 missure, such as exists in certain of the lower mammals, as the 

 rabbit and pig, and which represents, according to Gaupp ('00) 

 the taenia marginalis of reptiles. The upper border is concave 

 upward, and in its ventral portion there may be seen a small 

 incisure, open behind, formed by an overhanging, backwardly 

 projecting spicule from the uppermost part of the plate. This 

 incisure appears to be the representative of what Mead calls 

 the fissura laminae parietalis in the skull of Sus, where it is quite 

 conspicuous. The upper border is continuous above with the 

 membrane covering the brain. 



The lower border is continuous ventrally with the otic capsule 

 at the upper edge of the capsulooccipital fissure. Behind this 

 it follows the elongated occipitoparietal groove (figs. 1 and 5) 

 which runs backward to the dorsal occipital prominence, and 



