PECULIARITIES OF THE HUMAN SKELETON. 37 



skulls of other mammals, namely, the superior maxillaries 

 and the pre-maxillaries. Behind the superior maxillaries 

 are the palatals, which form the back part of the palate, and, 

 by means of ascending portions, join together the superior 

 maxillaries and what are called the pterygoid processes 

 of the sphenoid bone, two processes projecting downwards 

 from the base of the skull. It may also be mentioned that 

 the inner parts of these processes, namely, the internal ptery- 

 goid plates, are separate bones in most animals. The superior 

 maxillaries send up a pair of processes to the frontal bone, 

 behind the two nasals, the bones forming the ridge of the 

 nose ; but they get a much stronger support from a pair of 

 cheek bones, the jugals or molars, which project outwards 

 from them, and each of which sends one process up to the 

 frontal to complete the outer wall of the orbit, and another 

 backwards to form an arch with what is called the zygomatic 

 process of the temporal. The other bones of the face are 

 two little plates called lachrymals, grooved for the nasal 

 ducts, the passages by which the tears are carried from the 

 eyes into the nose ; and the inferior turbinated bones, a pair 

 of thin curved laminae which project into the nasal fossae. 



20. Peculiarities of the Human Skeleton. The most 

 remarkable peculiarities of the skeleton of man, as compared 

 with other animals, are connected with the maintenance of 

 the erect posture. 



The foot has a broad sole, and is arched both from behind 

 forwards, and also from side to side, so as to give elasticity 

 to the step. 



The straight position of the knee is characteristically 

 human, no other animal but man being supported on ex 

 tended knee joints; for though birds are also bipeds, thej 

 have the knees flexed in standing. The human knee joint 

 is so constructed that, when fully extended, it remains in 

 that position without muscular exertion, so long as the 

 weight of the body presses clown on it. And this can easily 

 be demonstrated; for the patella is situated in the tendon of 

 the extensor nmscle of the knee, and when it is loose, that 

 muscle is evidently relaxed : now, when one stands with the 

 knees straight, the patella can be felt with the hand to be 

 hanging perfectly slack; but as soon as the foot is lifted 



