Development of the branchial apparatus in rat, pig and chick embryos.

ABSTRACT

Serial sections of 4-6 mm rat embryos were carefully studied in relation to the serial sections of 36-somite chick embryos and 10 mm pig embryos under a low-power microscope to compare the development of their branchial apparatus. Four pairs of the branchial arch could be clearly identified in the 4 mm rat embryos, the first two being more prominent than the others. The aortic sac or the ventral aorta, the continuation of the truncus arteriosus, is located between the right and left hyoid arches. The thyroid diverticulum passes the aortic sac to attain its final position at the caudal region. Each aortic arch branches from the aortic sac and passes through the mesenchyme of each branchial arch to join the dorsl aorta. The branchial apparatus of the 4-5 mm rat embryos is highly similar to that of the 36-somite chick embryos and 10 mm pig embryos. Since the rat embryos are very easy to obtain for slide preparation, there is no significant problem in the use of rat embryos to study the development of the branchial apparatus instead of the pig embryo.