70 THE HUMAN SPECIES 



vertebrae, and it is not uncommon to meet with cervical ribs 

 proceeding from the last cervical vertebra. 



The sternum, or breast-bone, which, it must be remembered, 

 in our early progenitors consisted of a series of consecutive 

 parts, in all mammals, may be divided into three parts : hilt, 

 blade and ensiform process ; but in man, as in the rest of the 

 Primates, it forms a uniformly broad, compact plate. The 

 interarticular cartilages correspond to the lateral parts of the 

 episternum of the other mammals. 1 



The clavicle, or collar-bone, is developed in the same way 

 as in the mammals which employ the upper limbs for grasping, 

 scratching, flying, climbing or striking. The human clavicle 

 corresponds most closely in its development to that of the apes 

 and bats. 



A masterly and exhaustive treatise on the scapula has been 

 issued by Ranke. 2 In the quadrupedal mammals the scapula 

 forms the point of support for the upper limbs and consists of 

 a long, almost triangular bony plate with a relatively deep cup- 

 like cavity (the glenoid cavity) at its outer angle. 



Into this cavity the head of the humerus fits, producing 

 thereby an almost perpendicular upward pressure. The surface 

 modelling of the shoulder-blade is modified, on the one hand, 

 by the mechanical action of supporting the arm, and, on the 

 other hand, to an important degree by the muscles. The 

 shoulder-blade is further strengthened by the thickening of the 

 edges converging towards the glenoid cavity, and also by the 

 spine of the scapula, which in many mammals (e.g., the carni- 

 vora) runs midway between the two edges of the scapula 

 towards the glenoid cavity. 



The spine of the scapula indicates the direction of the main 

 pressure, forms the chief support and is situated perpendicularly 

 to the middle of the joint (Figs. 25-31). The closest resem- 

 blance to the human shoulder-blade is found in the orang, 

 gorilla, and chimpanzee ; that of the hylobates is intermediate 

 between the anthropoids and the cynocephalous apes. The 

 anthropoid scapula differs from the human in the following 

 respects (p. 71). The incisura scapulas is absent. The posterior 

 border of the human scapula takes a downward perpendicular 



1 Wiedersheim, loc.cit., p. 49. *Corr.-Blattf. Anthrop., 1904, p. 139. 



