8 C. W. M. Poynter 
He prepared diagrams illustrating the supposed fate of the arches, 
see fig. 4, which have since been quite generally employed. 
Zimmerman (1889), acting on the suggestion of Boas, exhib- 
ited a reconstruction of a 7 mm. human embryo showing a ves- 
sel, not previously described, between the fourth and pulmonic 
arches ; it was described as being about as large as the fourth arch 
and opening into that arch at both ends. Later the same year 
he found indications of such a vessel in an incomplete series of a 
sheep embryo and a complete vessel in a rabbit of the eleventh 
day, in the latter the vessel ran from the truncus arteriosus to 
the aortic root. 
Tandler (1902) made a study of rat and human embryos; in the 
former he found irregular vascular buds and in the latter, in 
two embryos, a vessel running from the truncus arteriosus to the 
aortic arch. He said, page 341: 
Da wir aber bei der Ratte so gut wie bei allen andern Sadugern einen 
funften Arterienbogen postuliren miussen, glaubte ich mich berechtigt 
diese Verbindung als ein Analogie des fiinften Bogens anzusehen, und 
dieses um so mehr als ja der ftinfte Aortenbogen bezugleich Ursprung und 
Verlauf bei den einzelen Species, ja bei den einzelen Embryonen, beispiel- 
weise beim Menschen, different zu sein scheint. ... Die Annahme, dass 
es sich hier um eine eigenthumliche Form eines fiinften Bogens handelt 
gewennt’ meiner meinung nach um so mehr an warscheinlichkeit, als ja 
dieser Bogen nicht nur sehr frith verschwindet, sondern sich auch sehr 
spat bildet. 
Lehmann (1905) in a study of the pig and rabbit found in the 
former a vessel connecting the fourth and pulmonic arches and 
joined with the aortic root. 
Locy (1906) reviewed the evidence in favor of a fifth arch but 
stated no positive conclusions although he was inclined to favor 
_ the idea of a true arch. 
Soulie and Bonne (1908) studied the mole and found a vessel 
connecting the truncus arteriosus with the pulmonary arch; they 
were very insistent in the claim of a true fifth arch and called at- 
tention to the exact resemblance to the present condition in 
selachians. They explained the development of the vessel after 
the pulmonary arch on the ground of the physiological impor- 
tance of the latter. 
236 
