310 MR. F. E. BEDDAKD ON THE [NoV. 3, 



(text-fig. 32, p. 309). It will be seen from that drawing that 

 three arches actually unite to form the median dorsal aorta, 

 and that all of these trunks are pervious where they join ; 

 there is not a question of an imperforate Ductus Botalli. The 

 injection has enabled me to ascertain this matter, and, moreover, 

 the arteries are so large that a dissection allows of the orifices 

 of the several tubes being seen with ease. The second and the 

 thii'd of the vascular arches are the first to join each other. The 

 common aorta thus formed gives off a thickish branch to the 

 muscles dorsally shortly after this junction. A little beyond this, 

 i. e. nearer to the middle line, the first, or Carotid, arch unites with 

 the common ti-unk. The aorta of each side of the body then gives 

 off a branch which perforates the musculature, and is that vessel 

 figured by Hyrtl * as running backwards through the transverse 

 processes of the vertebree. I have not, however, followed it 

 farther than into the first vertebra which it approaches. A little 

 after this the two aortae meet and become the single dorsal aorta. 

 This junction takes place at about the level of the anterior end of 

 the pericardium. The junction of the several aortic arches does 

 not seem to be accurately represented by Osawa. For a con- 

 siderable distance the aorta is closely adherent to the middle line 

 of the parietes, and indeed has even the appearance of being 

 sunk a little below it. It is covered with a sheet of fibrous tissue, 

 which has to be dissected away to expose the artery. This sheet 

 is apt to be a good deal pigmented. The aorta leaves its close 

 contact with the muscular parietes just before the transverse 

 membranes which tie down the two oviducts to the parietes, 

 which membranes come into contact in the middle line. At this 

 point, then, the aorta ascends on to a sheet of mesentery, and the 

 ascent increases as the abdominal region is entered, until finally 

 the distance of the aorta from the actual middle line of the 

 parietes is more than an inch. 



The four aortic arches inci-ease gradually in size, as might be 

 inferred from the sections through the median part of the 

 synangium and its two bi'anches. The Carotid is the smallest 

 and the Pulmonary the largest. 



The course of the Carotid arch is shown in the accompanying 

 drawing (text-fig. 33), which does not entirely agree with the 

 figure of Osawa t. When it has freed itself from the synangium, 

 it passes along more or less parallel to the next arch. It lies 

 anteriorly to the first of the branchial muscles and ultimately 

 joins, as has been already stated, the common aortic trunk. At 

 the point where it is most curved in its course it gives oif a strong 

 lingual branch (text-fig. 33, A) which runs foi'ward. This branch 

 is also attached to the carotid trunk by a perviotis connection 

 situated nearer to the root of the carotid, and thus allowing of a 



* Osawa {loc. cit. pi. xxxix., vert., & pi. xlii. fig. a, vert.) represents this artery 

 as arising from the afferent carotid arch in one figure and from the efferent second 

 arch m the other. 



t Loc. cit. pi. xxxix. 



