. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. The first period, previous to any change having- taken place in the branchiae, is given in fig. 18. Four pairs of trunks (1, 2, 3, 4) go off from the heart. The first branch on each side (1) gives off a small anastomotic branch (5); after which it becomes divided into numerous branchial filaments (6); these, by their ulti- mate subdivision, terminate in a capillary tissue or network (7), from which arise other minute returning vessels, forming, by their junction, a single large vessel (9), which brings back blood into th
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. The first period, previous to any change having- taken place in the branchiae, is given in fig. 18. Four pairs of trunks (1, 2, 3, 4) go off from the heart. The first branch on each side (1) gives off a small anastomotic branch (5); after which it becomes divided into numerous branchial filaments (6); these, by their ulti- mate subdivision, terminate in a capillary tissue or network (7), from which arise other minute returning vessels, forming, by their junction, a single large vessel (9), which brings back blood into the general circulation after it has been aerated in its course through the branchiae. The second branch (2) also gives off a small one (14) previously to its subdivision in the second branchial leaflet, which branch enters the returning vessel; thus producing a com- munication between the two vessels 2 and 9, as in the former case. The returning vessel then terminates in the arch of the aorta, in which the two vessels 13 and 15 also terminate. The third principal vessel (3) is similarly distributed on the third branchial leaflet, and the corresponding returning vessel (16) termi- nates in the aorta, as in the other case. The arch of the aorta, thus formed, gives off a branch (21), which, after receiving the fourth branch from the heart (4), goes into the lungs (19). The second period, shewn in Jig. 19, occurs Fig. * Tabular view of the circulation in vertebrated animals. VOL. I. when the branchiae begin to contract. The anastomotic branch (5), shewn in the former figure, is not much enlarged, and assumes the character of a continuous trunk with 1. The branches (11 and 12) have increased in size, but the original continuation of 1 going to the bran- chiae, has decreased in the same proportion. The anastomotic branch (14) has acquired the size of the arch of the aorta, whilst the continuation of 2 is diminished, and the branchial leaflet is contracted in a corresponding degr
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