Embryological development of the arterial system of the forelimb in Tupaia

The arterial system of the upper extremities in man shows drastic developmental changes and many individual variations related to interspecific variations in primates. The ontogenetic development in Tupaia was examined from the viewpoint of comparative embryology.

Histological specimens of 39 embryos were observed and reconstructed in three dimensions using a computer program. Four adult animals were dissected and examined with angiography to ascertain the end stage of development.

At the proximal end of the upper arm the deep brachial artery appears first as a concomitant vessel with the radial nerve. It becomes reduced in size and is succeeded by the posterior circumflex humeral artery, which is accompanied initially by the axillary nerve and finally by the radial nerve. The main arterial passageway to the fingers consists of the brachial and interosseous arteries during early development. The superficial brachial artery and median artery are formed later, and their connection becomes the main route of blood supply for the finger arteries up to the adult stage. The ulnar artery is formed at the end of arterial development to form the ulnar end of the superficial palmar arch. The superficial antebrachial arteries are also recognized.

All the arterial elements of the forelimb in Tupaia are observed in a variety of primates, including man, and the characteristics of Tupaia are thought to represent the primitive conditions of the common ancestor of tree shrews and primates.