300 



2°. Tlie processus coracoïdeus has eomparativel}' decreased, the 

 processus acroiiiialis, on Ihe otiier- hand, has increased. It a[)pears, 

 then, that the processus coracoïdeus, which is phylogenetically the 

 oldest part, is most strongly developed in the youngest stage, where- 

 as the processus ucroniialis, which is phylogenetically younger, comes 

 more to the fore in the older stages. The joint-cavily now lies for 

 the greater part on tiie planum scapulae. 



3°. The margo vertehralis consists of a shorter upper portion and 

 a longer lower portion. They are a( an obtuse angle to each other. 



V. The portion of the scapula from which afterwards the fossa 

 supraspinata develops, makes an angle with the future suhspinal 

 portion. This deviation of the upper part, which also occurs in the 

 adult shoulder-blade (since fossa supra- and infiaspinata do not lie in 

 one and the same plane), had not yet taken |)lace in the 16 mm. embryo. 



5°. In the cranial part of the shoulder blade a foramen occurs 

 under the angulus supeiior, which extends at Ihe costal |)lane of 

 the scapula as a groove along the margo superior in the direction 

 of the joint-cavity. In fig. 3 we give a cross-section of this foramen, 

 which is filled with connective tissue. 



The existence of this foramen is no doubt surprising; yet it was 

 not entirely unknown, as already Ruthkkfohd has described it (1. c). 

 However, according to this author it proceeds in a groove, which 

 reaches' as far as Ihe margo vertehralis. Now, in all the serial sections 

 in which I also met with a groove as well as with the foramen, it 

 proceeded along the margo superior in the direction of the joint-cavity. 



RuTHKRFORD explains ihis foramen as follows. He considers the 

 part of Ihe scapula, cranial to the foramen (resp. groove), as a 

 separate piece of cartilage, which he terms praesra[)ula. and which, 

 according to his account, is connected by a strand of mesenchyma 

 tissue with the sternal half of the clavicula. In this way he believes 

 an inner shoulder-girdle to have developed, while he supposes the 

 acromion-clavicula to build up the outer girdle. He adduces various 

 arguments to prove this; however, they are weak. In my judgment 

 the hypothesis is of no value, because a connection of the so-called 

 praescapula with the sternal half of the clavicula does not occur. 

 At all events in my preparations I never found a cell-strand like 

 the one described by Rutheiiford. 



This foramen is not present in all cases, lis development also 

 differs with various individuals, as shown by Ihe following data. I could 

 establish its presence either as a true foramen, or as a deep groove in 

 human embryos of the length of 16, 17.5, 18, 19.6, 21, 22, 25 

 (see fig. 3), 26, 27, 56, and 90 mm. On the other hand I did not 



