TRANSACTIONS OF SECTION D. 651 



sac also. Professor Robinson of Chicago has suggested that fluid pressure is a 

 powerful aid to friction iu producing bursffi. With this view his evidence will 

 induce most people to concur. 



8. The Connection of the Anterior Inferior Angle of the Parietal Bone 

 in Primates. By Professor R. J. Anderson, M.D. 



The extension of the parietal bone has evidently so important a bearing on the 

 development of the brain that its dimensions are regarded as important aids in 

 estimating the grade of the animal. The breadth of the bone compared with the 

 length becomes also remarkable in the higher types. 



Notice the antero-posterior diameter in Strix, which is to the lateral as 9 : 10. 

 The frontal is scarcely involved in this broadening in proportion to its breadth. 

 The length to the breadth is 25 : 10. But this superficial increase, as in Gallus, 

 if taken as an index of brain growth, is delusive, for the thickness of the bone is 

 considerable. The parietal iu a young ostrich is almost as thick as it is long, 

 and gives a thickness of 12 mm. to a length of 14 mm. The length of the brain 

 cavity is 18 mm. In fishes the discrepancies are of course further increased by 

 the accumulation of excessive growth of the skidl and the fiuid which reacts, so 

 that the skull ceases to be an index of the brain inflation. It is evident that in 

 the highest types the occipital and frontal supplement the parietal efticiently. 

 The interparietal itself is perhaps an occipital element (Meckel). The parietal is 

 4*2 cm. in Capybara compared with length of cavity of 9-5. The side con- 

 nections of the parietal become of great moment in the highest groups. Sphe- 

 noidal alse and squamosal aid the parietal to a varying degree. It is of 

 importance of course to bear in mind the various functions allocated to sphenoidal, 

 temporal, and even frontal before the parietal has yet joined them. So that 

 progress of ossification is apt to be aflected diSerently in different groups and in 

 different members of the same group. The portions of the parietal and temporal 

 covered by the temjyornlis have evidently a force that tends to bring these bones 

 into unison, but in its early associations the squamous is materially different. 

 The alse of the sphenoid are even less concerned, and the diversion of ossific 

 material appears to take place with greater facility, and in the lines of suture 

 of the parietal remain long incomplete, especially at the .angles. It is, however, 

 remarkable that the lines of suture are not more variable in position than they 

 are. A slight modification in position may perhaps not be regarded as of great 

 significance. But any variation that leads to an alteration in the articulation o? 

 the anterior inferior angles of the parietals must be of importance. Taking a few 

 examples : — 



The Kangaroo, Dugong, Leo, Ursus polaris, Hysena, Canis, Cystophora, Felis 

 catua, Galago, Lemur, Mycetes, Oebus, Pithecia, Hapale, Gorilla (?), Orang, Man, 

 Macacus rhesus (some), Semnopithecus entellus (some), Hylobates hainanus, all 

 have a parieto-sphenoidal articulation. The articulation varies in length ; in a 

 Mycetes it was f inch. 



The following, viz., Orang (?), Hylobates miilleri. Homo (occasional), Semno- 

 pithecus obscurus and entellus (some), Macacus cynomolgus (some), Macacus 

 rhesus (some), have not parieto-sphenoidal sutures. 



The following, Loris gracilis, Semnopithecus leucoprymnus. Gorilla (?), have 

 a parieto-sphenoidal suture which is not well marked and is sometimes reduced to 

 a point. 



