404 
DE. M. TONGE ON THE DEVELOPMENT OE THE SEMILTJNAE 
23. The complete closure of the infundibular aperture takes place about the end of 
the eighth day of incubation. 
24. The fifth vascular arch on each side gives off the branch to the lung of that side, 
and becomes ultimately the corresponding branch of the pulmonary artery, according to 
the view long ago propounded by Yon Baer. 
I cannot conclude without thanking several kind friends for assistance received from 
them during the preparation of this paper, which I here beg leave to acknowledge. In 
particular Dr. Beale, who suggested the best mode of heating the incubating-apparatus, 
and has given me much valuable advice ; the Rev. George Kempson and my cousin 
Mr. Charles Paddison, who sent me abundant supplies of fresh eggs ; and Dr. Cayley, 
who has kindly revised the translations from the German authors referred to. 
Explanation op the Plates. 
PLATE XXXI. 
The drawings (with the exception of figs. 37, 38, 39) are all copies of preparations,. 
They were made with the aid of the camera lucida, the preparations being all viewed 
by transmitted light, and variously magnified from 24 to 59 diameters. 
Fig. 1. Heart and branchial arches in situ, from the Chick at the middle of the fourth 
day of incubation, showing the convoluted tubular form then possessed by the 
heart. 
a. Auricle, b. Ventricle, c. Truncus arteriosus, d. Branchial arches. 
e. Pericardium. 
Fig. 2. Heart and a portion of the branchial arches of Chick at the 106th hour of incu- 
bation. The left side of the heart and truncus arteriosus is seen in the 
drawing. 
a. Truncus arteriosus, b. Ventricle, c. Rudimentary aorta. d. Rudi- 
mentary pulmonary artery, e. Septum forming between rudimentary aorta 
and pulmonary artery, f. Opening into ventricle. 3, 4, 5. Third, fourth, 
and fifth branchial arteries respectively. 
Fig. 3. The same preparation viewed on its anterior surface. 
g. Forked lower margin of arterial septum, h . Edges of groove between 
anterior valve-rudiments. 
Other letters the same as in fig. 2. 
Fig. 4. Diagram of branchial end of truncus arteriosus at the 106th hour of incubation, 
to show the part at which the sections drawn in figs. 5, 6, and 7 are made. 
Fig. 5. Cross section of truncus arteriosus of Chick at 106th hour of incubation, made 
in the line 1, 1, fig. 4, showing the shape of the channels of the rudimentary 
aorta and pulmonary artery, separated by the nearly horizontal septum. 
a. Aorta, b. Pulmonary artery. 
