Twenty-four human legs were dissected macroscopically to study the morphological details of the accessory deep peroneal nerve. This nerve arose from the superficial peroneal nerve and descended in the lateral compartment of the leg, deep to peroneus longus along the posterior border of peroneus brevis. Approaching the ankle joint, this nerve passed through the peroneal tunnels to wind around the lateral malleolus ; it then crossed beneath the peroneus brevis tendon anteriorly to reach the dorsum of the foot. The accessory deep peroneal nerve was found in every case examined and constantly gave off muscular branches to peroneus brevis and sensory branches to the ankle region. In addition, this nerve occasionally had muscular branches to peroneus longus and extensor digitorum brevis, and sensory branches to the fibula and the foot. The anomalous muscles around the lateral malleolus were also innervated by this nerve. Neither cutaneous branches nor communicating branches with other nerves were found. The present study reveals that the accessory deep peroneal nerve is consistently present and possesses a proper motor and sensory distribution in the lateral region of the leg and ankle. It is not an anomalous nerve as has previously been suggested.

In one case accompanied by congenital partial absence of the pectoralis major muscle the sternalis muscle was examined to confirm its innervation by means of analysis of intramuscular nerve distribution. It was proved that the sternalis muscle was supplied only by the pectoral nerves even in the case of sternalis in direct contact with the proper thoracic wall. These findings as well as the results of Ura (1937) and Morita (1944) favor the interpretation presented by Eisler (1901), in which the sternalis muscle was described as being supplied only by the pectoral nerves. However, the problem of double innervation of the sternalis requires continued discussion because the relationships between the pectoral nerves and the branches of the intercostal nerves or extramural nerves (Yamada & Mannen, 1985; Kodama et al., 1986) have not yet been resolved. The precise genesis of the sternalis muscle should be also examined though it has already been proved to be derived from the pectoralis muscle group including the subcutaneous trunci muscle.

The macroscopic branching pattern of the peripheral nerves is usually provided by the epineurial connective tissue, whereas the removal of the epineurium discloses component fascicles covered by a perineurial sheath comprising a fine network with a peculiar branching pattern. In order to compare both patterns, the common peroneal nerve (PC) was dissected minutely in 10 human legs. At the epineurial level the branching pattern into tributary bundles was variable in respect to both the origin of the superficial peroneal nerve and that of the muscular branches (Rr. m. peroneus longus, RPL) to the peroneus longus. At the perineurial level the fascicles formed intricate tiny plexuses without a discrete branching pattern, but as a whole consisted of a regular arrangement divided into four crural streams for the deep peroneal (PP), the accessory deep peroneal (PPA) and two dorsal cutaneous nerves. The RPL fascicles were derived substantially from the PPA stream. The findings on the fascicular branching pattern in the present study show that the PC consists of two muscular and two sensory streams that were ensheathed by the epineurium to form the PP containing a single muscular stream, and the superficial peroneal nerve with the three remaining streams. Thus the extensor and peroneal muscles of the leg have their own nerve supply from the PP and PPA, respectively. The branching pattern of the fascicles of muscular branches at the perineurial level may be a useful estimator of muscle grouping, for which the branching pattern at the epineurial level is hardly of any use due to its variability.

Iliocostalis (IC) muscles were studied in four dolphin embryos, three goat embryos and four Japanese adult cadavers through macroscopic dissection. The IC muscles of the dolphin were located on the lateral aspect of the trunk and displayed an intercostal arrangement. In contrast, the IC muscles in both the goat and human showed a double-layered architecture formed by a multisegmental muscle-tendon complex and were located on the lateral and medial sides of the costal angle, respectively. Generally, the nerve to the iliocostalis (NIC) in the dolphin and goat did not form a common trunk with the nerve to the longissimus on the epaxial plane, whereas in humans the NIC ran parallel to the nerve to the longissimus part of the way. The individual NIC ran caudolaterally, innervating the one lower (caudal) metameric division of the IC muscle in the dolphin and piercing the fascia of the IC muscles at a point in the next caudal intercostal level in the goat and human. In the upper thoracic part of the goat and human, the caudal shift of innervation was obscured, where the IC muscles were close to the vertebrae. The course of the NIC was closely related to that of the lateral cutaneous branch. The present study shows that the NIC is commonly destined for the one lower intercostal level among the three mammalian species, with their respective IC muscles having distinctly different structural complexity.

The branching and distribution patterns of the superior mesenteric artery were studied in 10 adult bullfrogs (Rana catesbeiana) after injection of coloured latex solution into the vasculature. The abdominal digestive organs in the bullfrog were mainly supplied by the coeliac artery and the superior mesenteric artery, both of which arose as a common trunk, the coeliacomesenteric artery, from the abdominal aorta. The coeliac artery supplied the stomach, liver, gallbladder and the pancreas, whereas the first branch of the superior mesenteric artery was the splenic artery with other branches supplying the greater part of intestine. The apex of the intestinal loop was defined as the region supplied by the trunk of the superior mesenteric artery, and its intestinal branches constituted a ' nested formation ' which had the following characteristics. (1) The branches of the trunk were distributed to both sides of the apex, and the distribution regions of younger branches were located more distant from the apex than those of older branches. (2) Two branches directed towards both sides of the trunk frequently made a common stem arising from the trunk. The second branch of the superior mesenteric artery constituted a secondary trunk and its distribution region could be defined as a secondary apex, since 1 of its branches also constituted a nested formation which was distributed to both sides of the primary and secondary apices. The intestinal branches of the superior mesenteric artery were divided into 4 types on the basis of their pattern of branching and course. It is suggested that the nested formation of the superior mesenteric artery in the bullfrog is a remnant of the vascular pattern of the tadpole, which possesses a double spiral mode of intestinal convolution, probably supplied by arteries with the nested formation in a latent form.