[The morphogenesis of the scapula of Tupaia belangeri].

The therian scapula was until now thought to show very primitive features during early morphogenesis, as are found in the scapula of adult monotremes (elevated position of the scapula, lack of a spina and a fossa supraspinata, laterally directed cavitas glenoidalis). A morphogenetic study of the scapula of Tupaia belangeri has proved some of these assumptions to be wrong. The scapula undergoes a tilting which shifts its angulus articularis cranially, but no descent of the scapula could be found. The supraspinous fossa, which was supposed to develop very late in ontogeny from the anterior border of the scapula (Lewis 1902, Cheng 1955), is present in Tapaiai from the start. Part of it ossifies in membrane. The scapular spine does not develop as a cartilaginous outgrowth from the anterior border, but is formed mainly as an appositional bone along the lateral surface of the scapula. The glenoid cavity and the humerus are initially directed laterally. They attain their definitive form after the heart has migrated downward and the arms have been adducted. This represents a true plesiomorphous character state in therian ontogeny.