Comparative anatomical studies on the thyroid and thymic arteries. V. House musk shrew (Suncus murinus)

The thyroid and thymic arteries were investigated in 36 male and 36 female house musk shrews. The superior thyroid artery was constant. The artery arose, in the most instances, from the external carotid arteries. The artery, in about one fourth instances, sent both the superior and inferior branches supplying the gland and the former branch terminated in the superior and inferior laryngeal arteries. The latter branch was independent in the remaining instances. The superior laryngeal artery was independent in a few specimens. In some instances, the superior thyroid artery did not send the inferior laryngeal which was the terminal branch of the tracheo-esophageal artery arising mainly from the subclavian and costocervical trunk. The middle thyroid artery was rare only appearing in one male specimen. The inferior thyroid and the thyroid ima arteries were absent in both sexes. On the other hand, the independent thyroid arteries arising from the external carotid, occipital, common carotid and internal carotid arteries appeared in high frequency (89% per body side in an average) in that order of frequency. Most of them may be some separated component of the superior thyroid artery. The middle thymothyroid artery was absent. The inferior thymic artery arising from the costocervical trunk or the internal thoracic (49% in an average) and the middle thymic artery arising from the subclavian (52%) shared the arteries supplying the intra-thoracic thymus. The supreme thymic and the superior thymic arteries were very rare, occurring in only one specimen, respectively. These results show that both the thyroid and thymic arteries in house musk shrews are very simple and seemingly basic, although there are some features characteristic only to this animal.