Vertebirata. Zoological Collections, 



descending on the left side of the oesophagus. The fourth arch on the 

 right, and fifth on the left side, appear to give rise to the pulmonary arteries* 

 In the mammalia, the ductus Botalli is formed, not as in birds or lizards, by 

 the permanence of the posterior part of the pulmonary arches, but by a 

 communication which remains in the bulb of the aorta, between the roots of 

 the pulmonic and systemic trunks.* Thus it is explained how the aorta of 

 birds corresponds with the right root of this vessel in lizards, and that of 

 mammalia with the left ; the arteria innominata of the left side being first 

 given off in birds, while, in mammalia, that on the right springs first from 

 the aorta. 



" From these observations, it appears that it is erroneous to compare the 

 single heart of fishes, or batrachia, with the right side, or pulmonary cavities 

 of the heart of higher animals. They are similar, it is true, in this respect, 

 that they both propel the blood into a respiratory organ ; but the relation of 

 the gills differs widely from that of the lungs to the heart ; and it would be 

 more correct to compare the single heart of fishes with the whole heart of 

 the higher animals though divided, or with this organ in the early stages of 

 their foetal development." — JE^idinbumh New f^kUo&qphmqUournaL AprU, 



*i'"'^ *' • Explanation of the Figures. 



"'^Fi^. li — The organs of circulation of the larva of the aquatic salamander, 

 magnified. From Rusconi — a, The heart ; h, the trunk which arises from 

 the base of the heart ; c, dilatation of this trunk in the form of a bulb ; 

 dddd, the four arches of the right side, three of which go to the gills, and 

 one opens into the artery which goes to the lung ; hhh, the three branchial 

 arteries ; e e e, communicating vessels between the branchial arteries and 

 veins ; i, union of the two internal branchial arteries into a single common 

 vessel ; /, pulmonary artery ; ot, vessel communicating between the common 

 carotid n, and that which is formed by the union of the two internal branchial 

 arteries ; q, continuation of the common vessel, and its union with its fellow 

 of the other side, from whence the aorta arises ; r, aorta ; x, auricle j 

 z, venous sinus. 



Fig. 2 — Diagram, from Burdach, reversed, shewing the branchial divisions 

 of the aorta of the chick on the lower side of the pharynx, and the mode of 

 their transformation into the aortic and pulmonary vessels. — a a, The carotid 

 arteries ; b b, communicating vessels of the branchial arches, which are obli- 

 terated ; c, the right root of the descending aorta ; c', the left, obliterated ; 

 d d, the pulmonary arches, or arteries ; e, ductus arteriosus ; 1, 2, 3, 4, 5, 

 branchial arches. 



Fig. 3. — Diagram of the branchial arches of mammalia, and their trans- 

 formations, corresponding with that of birds, by Biu-dach. From Dr A. 



* There is an approach to this form in the structure of the vessels rising from the heart 

 in some of the saurian reptiles. 



[[It has, in opposition to this view, been ingeniously suggested by our friend Mr Paget, 

 whose attention has been directed to this subject, in connection with inquiries into mal- 

 formations of the heart, that the ductus Botalli, or artei'iosus, in the mammalia, is 

 formed precisely as in birds and reptiles, viz. out of the posterior branchial arch, but on 

 the left side ; and we understand, that this, which was also the opinion of Baer, has since 

 been verified by Dr Thomson. We are, however, at a loss to understand what is repre- 

 sented by the " communication," which was observed by Dr Thomson to remain " in the 

 bulb of the aorta, between the roots of the pulmonic and systemic trunks," and at first 

 supposed by him to be the ductus Botalli, — unless it be explained by the following passage, 

 from a previous part of the memoir: — In the foetus of mammalia, after the division of 

 the aortic bulb into the systemic and pulmonic arteries, the " ductus arteriosus remains, for 

 some time, short and wide, and has the appearance of being an opening of communica- 

 tion between, or a deficiency in, the parietes of the juxta-posed tubes, (the aortic and 

 pulmonary roots j) it afterAvards becomes lengthened out and narrowed, and appears, 

 during a short period, to pass from the aorta to the pulmonary root and aorta continuous 

 with it ; but, about the tenth Aveek, in the human embryo, this part is dilated, and forms 

 a more direct communication between the ascending and descending aorta, and the ductus 

 Botalli is now formed by another part, viz. the end of the jiulmonary root, leading into the 

 arch of the aorta." There is, however, considerable ambiguity in the description. — Ed.] 



