DEVELOPMENT OF THE BLOOD VESSELS IN THE FROG. 189 



of the branchial vessels. His observations, which were based on 

 dissection, aided by injection of the vessels, deal only with the later 

 stages of larval development ; and his principal results are that both 

 the pulmonary and the cutaneous arteries arise from the fourth 

 aortic arch, the third arch being present in the earlier stages, but 

 atrophying about the time of the metamorphosis. 



In a subsequent paper Boas* notes that the carotid gland is not, as 

 has been very commonly assumed, a persistent and altered portion 

 of a gill, but is a structure arising altogether independently of the 

 gill vessels. 



By far the most important paper that has yet appeared on the 

 development of the Amphibian blood vessels, is one by Maurer,f 

 published two years ago. This is a very thorough piece of work, of 

 great value, and deals with the formation of the blood vessels from 

 their earliest appearance. Maurer's results were obtained chiefly 

 from the examination of continuous series of sections, and his paper 

 is illustrated by a number of excellent and exact figures. We had 

 made considerable progress with our work before becoming 

 acquainted with Maurer's description ; but from the time of our 

 doing so, we have found his paper of the greatest service. We shall 

 have occasion to refer frequently to Maurer's work, but it will be 

 convenient to give here a brief summary of his results. 



Maurer describes in each branchial arch two vessels, which he 

 names primary and secondary aortic arches, and which correspond 

 respectively to the arteres permanentes and arteres transitoires of 

 Busconi, and to the efferent and afferent vessels of our own account. 

 The primary aortic arches arise independently of the heart, and are 

 at first more or less lacunar. They acquire connections with the heart 

 and with the dorsal aorta before the appearance of the secondary aortic 

 arches, and so afford for a time a direct passage from the heart to 

 the dorsal aorta. 



The secondary aortic arches arise as direct outgrowths from the 

 divisions of the truncus arteriosus, and lie in the ventral parts of 



»Boas, "Beitrage zur Angiologie der Amphibien," " Morpholo-jisches Jahrbuch,' 

 viii.,1882, pp. 169-187. 



t Maurer, "Die Kiemen and ihre Defuse beiAnuren und Urodelen Amphibien, 

 " BforphologiflChee Jahrbucli," xiv., 1888, pp. 17o-222. 



