Slade.] *^^ [March 15, 



junction of the anterior transverse root, the remaining portion of the 

 arch being nearly of the same width. The breadth of the channel for the 

 play of the temporal muscle is proportionally large. The entire structure 

 of the arch, especially in its horizontal-vertical curvatures, exhibits enor- 

 mous strength. In the adult male all the cranial ridges attain their maxi- 

 mum size, thus presenting a largely increased surface for the origin of the 

 temporal muscle, while the relative greater breadth of the ascending ramus 

 of the mandible and the increased width of the pterygoid fossae are cor- 

 related with a corresponding development of the masseter and pterygoid. 

 The long and massive canines have reference to the powerful action of 

 the last named muscles, while their use has a sexual relation. The glenoid 

 cavity is transversely broader than in man, and more shallow, its anterior 

 boundary, formed by the anterior root of the zygoma, being scarcely 

 developed, thus allowing greater freedom for the antero-posterior move- 

 ment of the articulation of the mandible. 



In comparing the skull of the male gorilla with that of man, we shall 

 find that the arch of tHe former is not only vastly stronger, but the bones 

 present a different form and proportions. The squamosal is as long and 

 vertically as wide as the malar portion of the arch, while its upper border 

 rises into an angular form, constituting a very marked convexity, no trace 

 of which is to be seen in man. In the latter the jugal portion of the arch 

 decreases in depth after leaving the body of the bone, whereas in the 

 gorilla it continues of the same depth and is relatively longer. 



In the orang, the horizontal curvature of the arch is greatly produced, 

 and strongly developed at the portion corresponding to the malar-squa- 

 mosal suture. Its inferior border is flattened and thickened. The vertical 

 curvature, however, is not so great, while the channel for the temporal 

 muscle is relatively wider than it is in the gorilla. The crests and ridges 

 of the cranium, especially in the male, express the great energy of this 

 muscle, although the general outline of the arch is far lecS massive than 

 in the latter ape. 



The jugal arch of the chimpanzee presents much resemblance to that 

 of man, being narrow, and with slight curvature, either horizontal or 

 vertical. The malar is anteriorly flatter, and its orbital process is longer 

 and narrower at its base. The extent of surface for the development of 

 the temporal muscle is greater than in man, and the width of the channel 

 relatively increased. 



The slight modifications observed in the arch of the gibbons, exhibit a 

 distinct tendency to those shown in the lower types of the Simiadre. In 

 the old-world monkeys, the arch takes on a sigmoidal curvature, thus pre- 

 senting upon its superior border, a slight convexity behind and a corre- 

 sponding concavity anteriorly. The extent of this curvature varies in the 

 different groups. In the new-world monkeys, the postglenoid process of 

 tiie squamosal is largely increased, while the remarkable extent of the 

 ascending portion of the ramus, both vertical and antero-posterior, has 



