Okajimas Fol. anat. jap., 46: 123-137, 1969 The Origin, Course and Distribution of Arteries to the Thumb, with Special Reference to the So-Called A. princeps pollicis By Takuro Murakami, Kenichi Takaya and Hiromu Outi Department of Anatomy, Okayama University Medical School Okayama, Japan The arteries of the thumb have been studied by numerous authors in their various aspects. However, their true disposition, especially their course in relation to the muscles, has not yet been fully demonstrated. Neither the classical works of T a n d 1 e r (1897) and A d a chi (1928), nor the comprehensive study of Coleman and Anson (1961) seems to give us sufficient informations. This is partly due to the considerable variability of the arteries ; namely in their origin, course and branching. Furthermore, varying nomen- clatures (e. g. Baum 1907) have caused conspicuous confusions and made our understanding rather difficult. The present study, planned to elucidate these conditions, is hoped to contribute to a better under- standing of the arteries of the thumb. The materials consisted of 90 hands* of the Japanese adult cadavers, most of which were injected with lead oxide suspension. The morphology of the thenar muscles and their nomenclature As the relations of the arteries to the thumb muscles are essential for a correct understanding of their course, we start with the mor- phology of the muscles. Here too, some confusions of nomenclature are found. Thus, the deep head of M. flexor pollicis brevis, which inserts into the radial sesamoid bone and its vicinity together with the superficial head, is sometimes regarded as a part of the oblique * The results obtained in 44 out of these 90 cases were read before the Associated Meeting of the Kinki and Chugoku-Shikoku Associations of Anatomists (cf. M u r a- k ami et al., 1966). 123 124 T. Murakami, K. Takaya and H. Outi head of M. adductor pollicis. In the present report, we adopt the nomenclature of Frobse and Frankel (1908). Namely, the flexor inserts into the radial side of the thumb, and the adductor into the ulnar side. However, according to some authors (F lemming 1887 ; D a y and Napier 1961), these two muscles may have, in some cases, accessory insertions, i. e. the flexor inserting into the ulnar and the adductor into the radial side. We dissected the hands carefully in this respect. The oblique head of the adductor and the deep head of the flexor brevis were commonly fused with each other in their proximal part, and the two muscles were discriminated only by their insertions. Sometimes we found in their muscle belly some cleavages, that did not lead to the boundary in the insertion. But a careful comparison of various conditions of the whole series observed, has led us to the conclusion that those cleavages, diverse in position and distinction from case to case, cannot be regarded as a consistent boundary of the two muscles. We, therefore, identify these muscles always by the insertion. Since the proposal of H e n 1 e (1871), the existence in man of the palmar interosseous muscle of the thumb (sometimes called the deep head of the flexor pollicis brevis)** has been widely accepted, although the description differs somewhat among authors. According to the previous authors, the muscle should be a fairly independent bundle, which originates from the first metacarpal bone and inserts into the extensor aponeurosis of the thumb. Indeed, in our materials, the adductor pollicis muscle had a small muscle slip, which, as the most dorsal and medial part of the muscle, originated from the shaft and the base of the first metacarpal bone and the tendinous arch, under which the first palmar metacarpal artery arose from the radial artery. However, as the muscle slip was completely fused to the dorsal aspect of the adductor muscle, we could not identify it as an independent muscle. The only criterion possible to discriminate the muscle bundle may be the course of the first palmar metacarpal artery. In the present paper we provisionally call that muscle bundle which originates radial to the artery "palmar interosseaus- like bundle" of the adductor pollicis. ** A detailed study of this muscle will be reported by one of the present authors (M urakam i, in preparation). Arteries to the thumb 125 General pattern of the arteries of the thumb and the so-called "A. princeps pollicis " As in the case of other fingers, the proper digital arteries (Aa. digitales propriae) of the thumb are well developed only on the palmar side, while the dorsal digital arteries are very minute except in rare cases. Two palmar arteries, Aa. radialis and ulnaris pollicis, run along the radial and ulnar margins respectively, and have in front of the shaft of the proximal phalanx under the tendon sheath of the flexor pollicis longus muscle a transverse anastomosis, sometimes of a considerable caliber. Their main source, however, is very variable from case to case. In most cases, a branch from the superficial palmar arch divides into two twigs, one of which (A. marginalis Fig. 1. Various patterns of the arteries to the thumb. In a) the first palmar metacarpal artery is fully developed (normal, type Ia) . In b) the branches of the superficial palmar arch are unusually developed. In c) one of the branches of the first dorsal metacarpal artery constitutes the princeps pollicis artery (type VIIb) . And d) shows type Ib. 1: the first palmar metacarpal artery 2: the radial terminal branch 3: the ulnar terminal branch 4: the radial circumflex (perforating) branch 5: the ulnar circumflex (perforating) branch 6: a branch of the first dorsal metacarpal artery 7: the first common palmar digital artery 8: A. marginalis palmaris radialis 9: A. radialis pollicis 10: A. ulnaris pollicis 11: the proximal transverse anastomosis 12: A. radialis indicis 13: the radial terminal branch of the second palmar metacarpal artery . 126 T. Murakami, K. Takaya and H. Outi palmaris radialis, often called A. radialis anastomoses with A. radialis pollicis. The other twig (A. digitalis palmaris communis I) bifurcates again and anastomoses with A. ulnaris pollicis and A. radialis indicis (Fig. 1, c) ; when the branch of the first palmar metacarpal artery to the index finger is well-developed, the twig seams to join the latter branch (Fig. 1, a). But usually the contribu- tion of these superficial arteries is not remarkable, sometimes almost wanting ; on the contrary, a deep artery, the first palmar metacarpal artery (A. metacarpea palmaris I), offers normally the principal supply of the palmar digital arteries of the thumb (Fig. 1, a). This is one of the terminal branches of the radial artery. It descends distally between the first metacarpal bone and the adductor pollicis muscle, and reaches to the level of the neck of the first metacarpal bone between the adductor and the short flexor and under the tendon of the long flexor. Then, it divides into two terminal branches. The radial terminal branch, joined by A. marginalis palmaris radialis, continues to A. radialis pollicis the ulnar one, after it has gained superficial position and received a branch of the first common palmar digital artery, continues to A. ulnaris pollicis. In some cases, when the first palmar inetacarpal artery is fully developed, it appears that the ulnar terminal branch anastomoses with or supplies A. radialis indicis (Fig. 1, a). Sometimes the first palmar metacarpal artery is weak or almost wanting and substituted by a dorsal artery with an unusual course. The term " A. princeps pollicis" has been used with different meanings. Sometimes it is quite the same as the first palmar meta- carpal artery in the strict sense, and sometimes it means, regardless of the origin and course, the largest source of the palmar arteries of the thumb other than the branches of the superficial palmar arch. For the sake of convenience we follow this wider definition. The first palmar metacarpal artery This artery, often called the princeps pollicis artery, accurately corresponds to the palmar metacarpal arteries of the other fingers (more strictly, to the " deep " group of these arteries, M u r aka m i 1969) in its origin, course and branching, as Tan d I e r (1897) and Coleman and Anson (1961) pointed out. Therefore, we adopt the above designation ***. *** Sometimes the designation is applied also to arteries of various origin (our princeps pollicis artery). Arteries to the thumb 127 The radial artery reaches the proximal end of the first inter- metacarpal space, with a few exceptions (in 6 out of 90 cases), where its main flow penetrates the proximal end of the second intermeta- carpal space. There it pierces a cleft between the heads of the first dorsal interosseous muscle and then, giving off the first palmar metacarpal artery, passes under the thin tendinous arch of the ad- ductor pollicis, which spans between the bases of the first and second metacarpal bones, to build up the deep palmar arch. It runs medially piercing those bundles of the adductor that originates from the second metacarpal bone. The first palmar metacarpal artery originates as one of the terminal branches of the radial artery, as the latter passes through the tendinous arch of the adductor. In the above-mentioned excep- tional cases likewise we found always a smaller branch, which took the normal course of the deep palmar arch and gave rise to the first palmar metacarpal artery. The artery descends distally along the ulnar-palmar surface of the first metacarpal bone under the cover of the "palmar interosseous-like bundle" of the adductor pollicis, and reaches between the adductor and the short flexor . In its course, the artery sends off some muscular twigs and a nutrient branch to the metacarpal bone (usually in its proximal half).