Katsushi Kawai

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.

Nerve fiber analysis on the so‐called accessory subscapularis muscle and its morphological significance

A rare muscular anomaly, so-called accessory subscapularis muscle, was found in the left axillary fossa of a 95-year-old male cadaver during a student dissection practise. The muscle arose near the lateral margin of the scapula from the surface of the subscapularis muscle and ran upward to fuse with the capsule of the shoulder joint via a tendon. It measured 1.0 cm in width, 7.0 cm in length and 1.5 mm in thickness, and was separated from the underlying subscapularis muscle by the axillary and inferior subscapular nerves. Macroscopically, the anomalous muscle received its nerve supply from a branch arising from the lower root of the radial nerve near the origin of the thoracodorsal nerve and entered the muscle from its ventral surface. Nerve fiber analysis showed that the supplying nerve originated from fibers of the dorsal element of C7 immediately cranial to the thoracodorsal nerve. These findings indicate that the present anomalous muscle might be close to the formation of the latissimus dorsi muscle in its derivation rather than the subscapularis muscle.

Communication between the axillary and radial nerves in the human upper arm

The communication between the axillary (Ax) and the radial (R) nerves, which was observed in eight upper arms from 602 arms of 301 Japanese cadavers, was studied to determine its origin and distribution. The brachial plexus and spinal segments contributing to the Ax and R in all cases where communication occurred had no distinct differences from those in cases having no communication. According to the direction, the communication is divided into two groups: the communication from the Ax to R (7 cases) and vice versa (2 cases). One specimen had both groups of communication. The origin of communicating branches in these groups extended into the overlapping area (C5 + 6) of the origin of the Ax with that of the R, mainly from the ventral layer of the posterior cord from C6. The distribution of the communicating branch varied in development according to specimens. The communication from the Ax to R has a tendency to invade, from proximally to distally, the distribution of the muscular branches of the R to the radial extensor muscles of the forearm including the supinator muscle. However, the development into the cutaneous branches has no distinct inclination. These findings in humans and some other comparative anatomical descriptions show that in phylogeny the radial extensor muscles of the forearm have a different origin from other extensor muscles of the forearm and have a close relationship with the Ax. Therefore, the communication between the Ax and R holds an important clue in clarifying the morphological significance of the extensor nerves and muscles of the forearm.

A schematic diagram showing the various components of the embryonic aortic arch complex in the retroesophageal right subclavian artery

A retroesophageal right subclavian artery, arising from the arch of the aorta as the terminal branch and passing dorsal to the esophagus, was found in five (1.2%) of 428 bodies donated for student dissection at Kumamoto University between 1993 and 2008. The presence of a retroesophageal right subclavian artery has been generally explained to be caused by the persistence of the normally eliminated part of the right dorsal aorta caudal to the seventh intersegmental artery and the disappearance of the normally patent right fourth aortic arch and the part of the right dorsal aorta cranial to the seventh intersegmental artery during the developmental process. However, the parts which remain or disappear are different in each case. With the aim of determining the portions eliminated or persisting and thereby gaining an understanding of the developmental process of the retroesophageal right subclavian artery in each instance, we made schematic diagrams showing the various components of the embryonic aortic arch complex as the prototype just before the anomaly occurred. Based on these diagrams, we conclude that immediately preceding the disappearance of the distal part of the right dorsal aorta and the dorsal part of the right sixth aortic arch, the third intersegmental artery was situated opposite to the fourth aortic arch and the seventh intersegmental artery was situated cranial to the point of junction of the right and left dorsal aortae.

Morphological study, by teasing examination, of the communication from the musculocutaneous to median nerves.

Nine specimens with communications from the musculocutaneous to the median nerves were investigated, by teasing examination, from their origins in the brachial plexus to their final destinations in nerve fibers. The nerve fibers of the communications were derived from the sixth and seventh cervical ventral rami of the spinal nerves. The distributions of the nerve fibers of the communications were divided into four types. In Type A, the nerve fibers reached the thenar muscles and the lateral digital nerves. In Type B, they reached the pronator teres or flexor carpi radialis muscles in addition to Type A. In Type C, they reached the anterior interosseous nerve area in addition to Type B. Finally in Type D, they also reached the distal muscle belly of the index of the flexor digitorum superficialis. It was revealed that there was a definite rule in the distribution of the nerve fibers in the communications from the musculocutaneous to median nerves. The area of the distributions was expanded in order from the thenar muscles to the flexor muscles of the forearm. The results in this study are useful for proper diagnosis and treatment of the peripheral nerve injuries involving the musculocutaneous and median nerves.

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.