242 Professor Clark on a Case 



succession. The pair of fissures anterior to the first branchial arch 

 afterwards becomes the mouth, whilst the bands which are bounded 

 by the first and second fissures afterwards becomes the lower jaw. 

 In man the branchial arches appear in the fifth or sixth week, 

 and exist only for a very short time. And here, as in the other 

 mammalia, in birds and in the higher amphibia, they undergo no 

 further development. In fishes, as is well known, they are res- 

 piratory organs which serve for the whole life of the individual, 

 and are gradually endowed with an apparatus of cartilage and 

 bone, admitting of numerous subdivisions on which the ultimate 

 branches of the vessels are spread. In batrachia, the vessels are 

 subdivided on membraneous productions of the soft branchial 

 plates, and exist only during the larva state, with the exception 

 of the Proteus and Siren where they are permanent. 



With respect to the branchial arteries from the aorta, some 

 disappear as far as their stems are concerned, whilst their 

 ramifications persist, and others persist entirely under certain 

 modifications. The following is the process in the chick where, 

 for obvious reasons, it has been most accurately observed. From 

 the simple cavity of the heart, at its anterior extremity which is 

 the bulb of the aorta, spring in succession five pairs of branchial 

 arteries. They arch round the beginning of the digestive cavity, 

 to attain the spine, and on either side of it coalesce to form a 

 single stem. The stems are the two roots of the aorta, which 

 unite lower down in the spine to form that vessel. The trunks 

 of the two first pairs soon disappear; whilst the arteries which 

 orignally sprung from them to supply the head are permanent, 

 as well as their posterior branches of communication with the 

 subsequent pair. When this occurs, the blood flows from the 

 heart, through the third, fourth and fifth pairs, to the roots of 



