The developnient and fate of the aortic arch complex has been studied and taught f o r many years. The work of Congdon ( ' B ) ,
Poynter ('16) and others has left but few gaps in our understanding of the morphological development of this system. Nevertheless, most presentations of both the normal and abnormal development of the great resscls leaving the heart are still based on the summarizing diagram of Rathke ( 1858), or some modification of it (see fig. 1). This diagram presents succinctly the various components of the aortic arch system, showing in diagrammatic form their original symmetrical pattern, and indicating which components persist and which have ceased to be recognizable in the adulmt.
ALEXANDEE BARRY
If one follows the generally accepted facts concerning the development of the aortic arch system, one can subdivide it into more recognizable components than those generally described. Ventral aoptic root between IV and 111 Aortic arch IV Vertebral artery Right subclavian art. ~nternal mammary a.J ee Aortic arch I l l Aoriic arch IV Aortic arch VI Dorsal oortic root segments 3 t o 7 Dorsal aortic root'segments 8 etc. Ventral aortic rod between aortic arches Ill BIV Ventral aortic root between oortic arches IV h VI Seventh dorsal intersegmental artery Longitud i na 1 onostomoses