Satoru Honma

Anomalous lumbrical muscles arising from the deep surface of flexor digitorum superficialis muscles in man.

During anatomy practice in 1999 at Kumamoto University School of Medicine, the anomalous lumbrical muscles originating in the forearm were observed in both arms of a cadaver. These muscles, originating from the intermediate tendon of the deep layer of the flexor digitorum superficialis for the index finger (FDS-II), passed through the carpal tunnel to join the insertion of the first lumbrical muscle, and formed a muscle belly near the origin in the left and at the insertion in the right. The left anomalous muscle was innervated by a branch of the median nerve just proximal to the carpal tunnel. The right one received a twig from the nerve to the first lumbrical muscle. Tracing the nerve fibers by peeling off the epi- and perineurium clarified that the nerve fibers supplying the left anomalous muscle formed a common bundle with the fibers to the first lumbrical muscle. Therefore, these anomalous muscles are considered to be the accessory lumbrical muscles arising from the forearm. The three accessory lumbricalis, including one case reported by Yamada (1986), received branches which had slightly different origins from proximally (nerve to the distal belly of FDS-II) to distally (nerve to the first lumbricalis). Accordingly the position of the muscle belly shifted distally. The occurrence of these unusual accessory lumbrical muscles indicates that the distal belly of FDS-III and the first lumbricalis are derived from a common muscle origin and presents an important clue to the phylogenetic origin of the flexor digitorum superficialis.

Inferior epigastric artery arising from the obturator artery as a terminal branch of the internal iliac artery and consideration of its rare occurrence

The origins of the inferior epigastric and obturator arteries and the relationship between these arteries have been determined macroscopically in examinations of 706 body-halves of Japanese subjects. Three very rare inferior epigastric arteries were found to arise from the obturator artery leaving the internal iliac artery. The intimate relationship between these arteries has been documented by the obturator artery arising from the inferior epigastric artery and the anastomosis between them. It is generally interpreted that such anomalies occur as remnant or partial disappearance of the connection between the pubic branches of the inferior epigastric and obturator arteries. The inferior epigastric artery arising from the obturator artery is also thought to be a similar anomaly. Since the obturator artery from the inferior epigastric artery represents one form of extreme anomaly, and the inferior epigastric artery from the obturator artery represents another form, it would seem that these two forms of extreme anomaly should occur at similar frequencies. However, in our research, the incidence of the former was 10.5% while that of the latter was a very low 0.4%. During normal development, the inferior epigastric artery is established at an earlier stage than the obturator artery as a channel for blood supply. We suppose that the difference of blood flow resulting from this time lag is one of the reasons why the inferior epigastric artery from the obturator artery is very rare in comparison to the obturator artery from the inferior epigastric artery.

Anatomical study of a left single coronary artery with special reference to the various distribution patterns of bilateral coronary arteries

A left single coronary artery of heart was observed during anatomy practice at Kumamoto University School of Medicine in a 73-year-old female cadaver who died from a thalamic hemorrhage. The left single coronary artery, having a single orifice in the left aortic sinus, bifurcated into the anterior interventricular (IVa) and circumflex (CIR) arteries. No orifice of the right coronary artery was found on the aortic wall. Giving off a branch which traversed the upper part of the infundibulum to supply the anterior upper region of the right ventricle, the IVa descended in the anterior interventricular sulcus to supply the apex of the heart. The CIR curved leftwards in the atrioventricular sulcus to reach the posterior surface, after which it continued to emerge again into the anterior surface. The atrial arteries showed no anomalous distribution pattern and histological observation revealed no pathological abnormality other than a slightly thickened tunica intima. Furthermore, we observed the distribution patterns of bilateral coronary arteries in 377 hearts dissected during anatomical practice over 13 years at Kanazawa University (1980-1986) and Kumamoto University (1993-1998). Although the reason why only the right coronary artery was absent is left unexplained, it was concluded that the left single coronary artery in this study, having the developed left conal and circumflex branches, was an extreme case of the left dominant series of coronary arteries. The formation of single coronary arteries can be explained embryologically by the change of flow in the capillary plexus established on the ventricle wall.

Left inferior vena cava with regressed right inferior vena cava

A left inferior vena cava was found in the cadaver of an 88-year-old Japanese man during a student dissection course at Kumamoto University School of Medicine. The right common iliac vein ascended obliquely toward the left behind the right common iliac artery and united with the left common iliac vein to form the inferior vena cava in front of the fifth lumbar vertebral body behind the left common iliac artery. The inferior vena cava ascended on the left side to the aorta, and after the left renal vein joined to it at the level of the third lumbar vertebral body, it turned obliquely to the right and crossed superficially to the aorta. At the right side of the aorta, the common stem of the third lumbar vein and the posterior renal vein was joined to the oblique part. The inferior vena cava then ascended, receiving the right renal vein as it would normally. The inferior vena cava is thought to develop symmetrically but this left inferior vena cava shows a persistence of the left channel of the infrarenal part, which normally disappears. Although the common stem of the veins that joined to the oblique part on the right side did not continue to the right common iliac vein, gross anatomical findings suggested it to be the remnant of the right inferior vena cava.

Derivation of the anterior belly of the digastric muscle receiving twigs from the mylohyoid and facial nerves

The anterior belly of the digastric muscle is usually supplied by the mylohyoid nerve, and in general anatomy textbooks, the anterior belly is invariably described as receiving no other nerve except the mylohyoid nerve. In fact, however, it is sometimes supplied by a branch of the facial nerve in addition to the mylohyoid nerve. Such cases were found in 8 bodies or 9 head sides among 539 bodies or 1078 head sides of Japanese subjects. Those nine cases were investigated in detail and it was clarified that they had the following three characteristics in common: (1) the twig originating from the facial nerve appears as the twig of the stylohyoid branch in most cases, (2) the twig from the facial nerve enters the anterior belly on its lower (shallow) surface and the twig of the mylohyoid nerve on its upper (deep) surface, (3) the twig of the mylohyoid nerve is distributed to the deep region and the twig of the stylohyoid branch is distributed to the shallow region of the anterior belly. From these results, it was concluded that the anterior belly, receiving the twigs of the mylohyoid and facial nerves, had been formed by secondarily combining the most ventral and rostral part of the primordium of the stylohyoid muscle in the second branchial arch with the caudal part of the primordium of the anterior belly in the first branchial arch.

Radial artery running beneath the biceps tendon and its interrelation between the radial recurrent arteries.

A radial artery running beneath the biceps tendon was found in the cadaver of a Japanese woman during a student dissection course at Kumamoto University School of Medicine in 2006. The brachial artery bifurcated into the radial artery and the ulnar artery in the cubital fossa, and the radial artery twisted laterally running beneath the biceps tendon, and when it was situated laterally to the tendon, twisted distally at the level of the radial tuberosity, and then twisted medially again. After the radial artery passed over the biceps tendon, it turned distally and continued as a normal radial artery. The superficial brachial artery, which coexisted with the brachial artery, was given off from the axillary artery and it continued to the final twist of the radial artery. The course of this radial artery is similar to the arterial rings surrounding the biceps tendon, found during the same dissection course. The arterial rings were formed between the brachial artery and the radial artery, and their proximal origins ran beneath the biceps tendon, while the distal origins were superficial. The present arterial variation is thought to have occurred when the normal part of the radial artery in the cubital fossa was substituted by the arterial ring, coexisting with the superficial brachial artery, which usually disappears during normal development. Furthermore, it is suggested that a part of the arterial ring always remains as a radial recurrent artery.

An aberrant axillary artery penetrating the origin of the radial nerve from deep to superficial

An aberrant axillary artery that penetrated the radial nerve from deep to superficial during its course, was observed. The brachial plexus in the present case was classified as the Adachis C-type brachial plexus. Further, an accessory radial root existed, which was a nerve bundle branching from the deep aspect of the inferior trunk and communicating with the radial root from the posterior cord to form the radial nerve. The axillary artery went on along the lower border of the brachial plexus and passed between the radial root and the accessory radial root from deep to superficial at its third section. As the axillary artery penetrated the origin of the radial nerve from deep to superficial, it was judged to reach deep under the posterior cord, hence deeper than the brachial plexus.

A histologic study of extralobar pulmonary sequestration and its anomalous artery as a clue to its development

In 1997, an anomalous small mass of soft tissue was found in the left thoracic cavity of a Japanese male cadaver during student dissection practice. It was linked only by branches from the thoracic aorta, hemiazygos vein and greater splanchnic nerve, with no connection to the normal lung by vessels or airway. Examination of cut sections clarified that this anomalous small tissue mass was an extralobar pulmonary sequestration (EPS). Many cases of pulmonary sequestration have been reported from the clinical aspect, but there are few from a purely anatomical viewpoint. In the present case, detailed gross anatomical and histologic observations clarified that the anomalous artery supplying the sequestration resembled an elastic artery. In view of the findings of other reports, the anomalous arteries are divided into two types, the elastic type such as the pulmonary artery and the muscular type such as the bronchial artery. So it is thought that the histologic observation of an anomalous artery in comparison with normal pulmonary and bronchial arteries may offer an important clue to consider in elucidating the origin and development of pulmonary sequestration.

Right ligamentum teres joining to the right branch of the portal vein

Ligamentum teres joining to the right branch of the portal vein in a 79-year-old Japanese male cadaver was noted during student dissection at Kumamoto University in 2004. The ligamentum teres entered the liver along the left side of the gallbladder fossa. The quadrate lobe was not distinguished from the left lobe in the visceral surface. When the liver parenchyma was removed by tearing off to expose the branches of the portal and hepatic veins, it was clarified that the ligamentum teres unusually joined to the bifurcation of the upper anterior and lower anterior branches of the right branch of the portal vein. The ligamentum teres is the remnant of the umbilical vein working throughout fetal life. Initially a pair of the umbilical veins entered the sinus venosus. During the fourth and fifth weeks they connect to the hepatic sinusoids, which become the portal and hepatic veins, and the parts entering the sinus venosus of both umbilical veins disappear. By the eighth week, as all remainder of the right umbilical vein disappears, the left umbilical vein is the only one to carry blood from the placenta to the liver. It results in the ligamentum teres joining to the left branch of the portal vein. However, in the present case it is thought that the right umbilical vein remained instead of the left one for some reason, and it then became the right ligamentum teres joining to the right branch of the portal vein.

The superficial brachial artery passing superficially to the pectoral ansa, the highest superficial brachial artery (Arteria brachialis superficialis suprema)

The human superficial brachial artery passes superficially to the median nerve and can be classified into three subtypes according to its topographical relationship to the pectoral ansa. When the superficial brachial artery passes superficially to the pectoral ansa, it is defined as the highest superficial artery. We found the highest superficial brachial arteries in both arms of a single cadaver. The right one coexisted with a normal axillary artery, and its identification was not difficult. The left one ran medially to the brachial plexus proximally and became superficial to the brachial plexus after branching off the artery, which gave the subscapular artery, then passed between the radial nerve and its accessory root from deep to superficial and ended as an inferior collateral ulnar artery. We also found a muscular axillary arch in each of the arms, both of which were innervated by the medialmost branch from the pectoral ansa. The right highest superficial brachial artery passed deep to the nerve to the muscular axillary arch. We conjectured that the left axillary artery is where the highest superficial brachial artery, as found on the right, coexists with the axillary artery in the case of Adachi’s C-type brachial plexus (AxC). Then, the highest superficial brachial artery develops as a main stem, and the latter remains as a rudimentary AxC. Because the left axillary artery is caught on neither the pectoral ansa nor its branches, the left axillary artery can shift medially to the brachial plexus, and its true form is not obvious.