480 



MAMMALS. PHYLUM CHORDATA 



of application of his weight, as well as a host of other modifica- 

 tions of musculature and skeleton. The opposability of the big 

 toe has been lost, but that of the thumb has increased to a greater 

 degree than is found in any apes ; at the same time the radius 

 can be rotated round the ulna (Fig. 349). There is a very high 

 degree of tactile sensibility of the palmar surface, and an extra- 

 ordinary sensitivity of the proprioceptors in the muscles and 

 joints, so that we know without practice the position of the tip 

 of the index finger, and the two index fingers can be made to 

 meet blindfold in any position in space which they can reach. 



The changes in the skull (Fig. 369) 

 may be connected with the in- 

 creased size of the brain, the adop- 

 tion of a less actively carnivorous 

 diet, and the upright posture. The 

 brain case is greatly enlarged, the 

 jaws are shortened, and the foramen 

 magnum comes to lie underneath 

 the skull. There is considerable 

 fusion of bones ; in the adult the 

 four occipital bones and the inter- 

 parietal form a single ring ; the 

 basisphenoid, presphenoid, ali- 

 sphenoids, orbitosphenoids and 

 pterygoids form a single sphenoid 

 bone, which later ankyloses with the 

 occipital ; there is a single ethmoid, 

 representing mesethmoid, turbinals and vomer ; the periotic, 

 squamosal and tympanic unite to form a temporal bone ; and 

 the premaxillo-maxillary suture almost or completely disappears. 

 In the sutures of the cranium there may be small irregular 

 Wormian bones. The projection of the dentary which forms the 



2123 



chin is a distinctive human feature. The dental formula is ; 



2123 



the canine, although it remains pointed, is only very slightly 



longer than the incisors, and the last molar, or wisdom tooth, 



quite often does not cut the gum. The pattern of the cheek teeth 



is bunodont, that is, there is a set of rounded cusps suitable for 



an omnivorous habit. Man has no tail, but three caudal vertebrae 



are present (Fig. 370). 



One of the most striking features of man is his nakedness, 



m^' 



jSBBf 



Fig. 370. — The coccyx, or ves- 

 tige of the caudal vertebrae of 

 man. — From Cunningham. 



I, 2, Transverse processes ; 3, for sacrum ; 

 4, cornu. 



