The branching pattern of the deep branch (ramus profundus) of the ulnar nerve and its relation with the target were analyzed in the human hand by an improved dissection method. After sending off branches to the hypothenar muscles, the r. profundus branched off an ulnar stem and a radial stem to the fourth, to the third and to the second intermetacarpal spaces, respectively, in this order, and an ulnar stem to the first to become terminal branches. The ulnar stems included an ulnar interosseous branch and a superficial articular branch in addition to a lumbrical branch in the third and fourth intermetacarpal spaces. The radial stems included only a radial interosseous branch. The branching pattern of the ulnar stems as well as its topographical relationship with the radial stems indicated a fundamental spatial arrangement of the branches in the intermetacarpal spaces: the lumbrical, superficial articular, ulnar interosseous and radial interosseous branches were arranged fundamentally in this order from ulnar to radial in each space; the first three branches may form a common trunk. The present observations demonstrate that individual nerves in the extremities may have a regular branching pattern, contrary to most of the previous observations.

The thenar and hypothenar muscles as well as their supplying nerves were analyzed with an improved dissecting method. Among the four thenar muscles, the m. abductor pollicis brevis (AbPB) has a separate muscle belly, whereas the m. opponens pollicis (OP), the superficial and deep heads of the flexor pollicis brevis (sFPB and dFPB), and the adductor pollicis (AdP) are fused with each other to make a single mass (deep thenar muscle group). These muscles are innervated by branches of the recurrent nerve and the accessory recurrent nerve from the median nerve as well as by terminal branches of the deep branch (ramus profundus) of the ulnar nerve. These three nerves frequently form a loop within the deep thenar muscle group (thenar loop), and a branch to the OP and one to deep parts of the sFPB often make a smaller loop (intrathenar loop) whereas the AbPB receives a separate nerve branch. Among the hypothenar muscle, the m. abductor digiti minimi and the m. flexor digiti minimi brevis are fused with each other, and their supplying nerves frequently form a loop in these muscles (intrahypothenar loop), whereas the m. opponens digiti minimi is separated from the others and receives a separate nerve branch. In the distribution pattern of supplying nerves to the thenar and hypothenar muscles, we find regularities in that they branch off in a regular manner from the ulnar and the median nerve, and that nerve branches to those muscles with fused bellies frequently communicate with each other to make loops.

ABSTRACT. X-ray examinations of Japanese monkeys (Macaca fuscata) in two groups on Awaji-

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