Comparative anatomical studies on the thyroid and thymic arteries. IV. Rabbit (Oryctolagus cuniculus).

The thyroid and thymic arteries were investigated in 30 male and 30 female Japanese white strain rabbits. Because of the high frequency (87% on average) of an independent superior laryngeal artery, the superior thyroid artery which arose either from the external or the common carotid artery was less common (13%). On the other hand, the middle thyroid artery was constant (99%); it always arose from the common carotid and penetrated the gland, supplying it, and terminated in the inferior laryngeal artery. The inferior thyroid artery was observed only in 1 female specimen; it arose from the common carotid, reached the gland caudally, and also terminated in the inferior laryngeal. The thyroid ima, arising from the brachiocephalic trunk, was found only in 1 male specimen. There were some independent thyroid arteries in about one fourth of body sides; they arose from the common carotid artery singly or together with the tracheooesophageal. A middle thymothyroid artery occurred in 1 male and 1 female specimen. The inferior thymic artery, arising from the internal thoracic or rarely from the costocervical trunk, was the most constant (92%). The middle thymic artery was also frequent (55%), arising from the common carotid, brachiocephalic trunk, aortic arch or the subclavian artery, in that order of frequency. The supreme thymic artery was present in 17%, on average, originating from the middle thyroid or directly from the common carotid artery. The superior thymic artery arising from the superficial cervical artery or the thyrocervical trunk was rare (5%). These results show that both the thyroid and thymic arteries in rabbits are more complex than in polyprotodont marsupials, rats and man, and that the thyroid arteries are simpler than in guinea pigs.