Multiple positional relationships of nerves arising from the sacral plexus to the piriformis muscle in humans]

The positional relationships between the piriformis muscle and the nerves which arise from the sacral nerve plexus were studied in 514 sides of 257 Japanese adults. These were classified into Types I-XIII and numerous subtypes based on: 1) the number of nerves perforating the piriformis muscle, 2) whether all or part of the nerve perforated the muscle, 3) the order of perforation and position in the muscle, and 4) communications between the nerves. In this paper, the multiple positional relations between the nerves and the piriformis muscle, the frequencies of the various types, and the order of priority concerning the perforation of nerves through the muscle are discussed. 1) The typical case, Type I, in which the piriformis muscle is not perforated by nerves except for a part of the superior gluteal nerve, was found in 309 (60%) of 514 sides. Types III-X, in which the muscle is perforated by additional nerves, were found in 195 sides (38%), and in 175 of these, all or part of the common peroneal nerve passed through the muscle. Types XI-XIII, in which the inferior gluteal nerve and other nerves pass above the piriformis muscle, were found in 10 sides (2%). Among all types, the following were generally seen: Type V, the piriformis muscle is perforated by both the inferior gluteal and common peroneal nerves; Type VII, the muscle is perforated by the two above-mentioned nerves and part of the posterior femoral cutaneous nerve (Fig. 16, Table 1). The common peroneal nerve followed two courses (a combination of over, through, and under the piriformis muscle) in 49 extremities. In the 4 cases of Type X (1%), the tibial nerve was divided into two components due to the intervention of the most caudal bundle of the piriformis or an unknown muscle. The dorsal component passed through the muscle, while the ventral component followed the typical course under the muscle (Figs. 9-11). Therefore, in the above-mentioned 53 cases as well as in other cases, the sacral nerve plexus cannot be divided into ventral and dorsal layers up to the sacral nerve roots, as in typical cases. Type II, in which the piriformis muscle is perforated by only a caudal branch of the superior gluteal nerve, was found in about 16% of 249 cases; this type was accompanied by some of the other types (Table 2). In the extraordinary case of Type XII with Type II, a branch of the superior gluteal nerve passed under the piriformis muscle (Fig. 13).(ABSTRACT TRUNCATED AT 400 WORDS)     

Martin-Gruber anastomosis revisited

Based on a study of 70 human cadavers (31 male, 39 female) and on cases described previously, we propose a new classification of the Martin-Gruber anastomosis, a neural connection between the median and ulnar nerves in the forearm. The anastomosis was found in 16 (22.9%) cadavers, being bilateral in three (18.7%) and unilateral in 13 (81.3%), five right and eight left. It occurred in eight (25.8%) of the 31 male cadavers and in eight (20.5%) of the 39 females. Therefore, the anastomosis was found in 19 (13.6%) of the 140 forearms. In Pattern I (89.5%) the anastomosis was made by only one branch, whereas in Pattern II (10.5%) it was made by two. The individual branches were classified as Types a, b, and c based on the nature of their origin from the median nerve. Type a (47.3%) arose from the branch to the superficial forearm flexor muscles, Type b (10.6%) from the common trunk, and Type c (31.6%) from the anterior interosseous nerve. Pattern II was a duplication of Type c (10.5%). The anastomotic branch took an oblique or arched course before joining the ulnar nerve, undivided in 15 cases, but divided into two branches in four cases. The anastomosis passed in front of the ulnar artery in four cases, behind it in six, and in nine cases it was related to the anterior ulnar recurrent artery.     

Nervous branch passing through an accessory canal in the sphenozygomatic suture: the temporal branch of the zygomatic nerve

A nervous branch which passes through a small canal in the sphenozygomatic suture is sometimes observed during dissection. To examine the origin, course and distribution of this nervous branch, 42 head halves of 21 Japanese cadavers (11 males, 10 females) and 142 head halves of 71 human dry skulls were used. The branch was observed in seven sides (16.7%); it originated from the communication between the lacrimal nerve and the zygomaticotemporal branch of the zygomatic nerve or from the trunk of the zygomatic nerve. In two head halves (4.8%), the branch pierced the anterior part of the temporalis muscle during its course to the skin of the anterior part of the temple. The small canal in the suture was observed in 31 head halves (21.8%) of the dry skulls. Although this nervous branch is inconstantly observed, it should be called the temporal branch of the zygomatic nerve according to the constant positional relationship to the sphenoid and zygomatic bones. According to its origin, course and distribution, this nervous branch may be considered to be influential in zygomatic and retro-orbital pain due to entrapment and tension from the temporalis muscle and/or the narrow bony canal. The French version of this article is available in the form of electronic supplementary material and can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00276-002-0027-4.     

The variable anatomy of the nerve to the extensor carpi radialis brevis

The origin and course of the nerve to the extensor carpi radialis brevis are closely related to the lateral aspect of the elbow joint and proximal portion of the radius—both of which are frequent sites of pathology and surgical treatment. The specific origin of the nerve supply to the extensor carpi radialis brevis muscle has been attributed variably by diverse anatomic and clinical texts to be the radial nerve, its deep branch or its superficial branch. This study was undertaken to determine the most common source of the nerve to the extensor carpi radialis brevis, as well as the most predictable topographic site of its origin. A total of 111 limbs were dissected, with the most common origin (56.7%) found to be the deep radial nerve, followed by the superficial branch of the radial nerve (31.5%), and least frequently from the bifurcation of the radial nerve into its superficial and deep branches (11.7%). This nerve branch was found to arise in most individuals within one centimeter of the distal edge of the humeroradial joint and to pass distally about 3.5 centimeters before entrance into the extensor carpi radialis brevis muscle. © 1993 Wiley-Liss, Inc.     

Morphological variability of the renal artery branching pattern: a brief review and an anatomical study

The segmental branches of the renal artery vary in number and origin. The 1998, Terminologia Anatomica homologates two branches of the renal artery (anterior, posterior) and five segmental arteries: four from the anterior branch and one from the posterior one. The purpose of this study is to evaluate the renal artery branching pattern, the number and origin of the segmental arteries, as well as to review data from similar studies. The study material consisted of 60 formalin-fixed adult kidneys. Dissections and microdissections were performed on the renal arteries and their branches. The branching of the renal artery was prehilar in 81.67% of cases, hilar in 10% and intra-sinusal in 8.33%. The number branches varied as follows: two branches in 42 cases (70%), three branches in 14 cases (23.33%) and four branches in four cases (6.67%). We subsequently analyzed the origin of the segmental arteries and found that in 53% of the cases the segmental arteries arose independently from the renal artery's branches, while in 47% of the cases they derived from common trunks of type I (85%) or II (15%). Type I trunks are those that originate directly from the main renal artery. They divide either into 2-3 segmental branches, or into just 1-2 branches and a smaller trunk (type II). The type II trunks further divide into 2-3 other segmental branches. These common trunks must be taken into account to avoid confusion with the segmental arteries. Knowledge of these variations is useful not only morphologically, but also clinically.     

Study on the subclavian artery and its branches in Japanese adults.

We examined the entire array of branches and the state of ramification of each branch of 144 subclavian arteries (Su) in 72 Japanese adults, and obtained the following findings. (1) The incidence of Type I -A(1) was 13.2%, the highest among the entire Su ramification. This was followed by Type I -B(1) at 9.0%, then Type I -A(2) at 6.9%, indicating considerable variation in the morphology of Su ramification. (2) Ontogenetic factors were implicated because of the existence of cases in which Su traversed the scalenus anterior muscle anteriorly (Type III: 0.7%), or was transfixed (0.7%). (3) Type 1-c was the form of thyrocervical trunk (Ttc) observed with the highest incidence of 31.3%. In addition, we propose that Types a-j (that were formed from a common trunk consisting only of the ascending cervical artery and inferior thyroid artery, and those in which another branch was included in this common trunk: 88.9%) be called Ttc. (4) The most common type of transverse cervical artery (Tc), which is formed from a common trunk consisting of superficial and deep branches, was found to be Type 1-a that branches from the first part of Ttc. It was observed with the highest incidence of 61.8%. Some of the superficial branches to the upper portion of the trapezius muscle that were independent and branched from Ttc (Types e, f: 2.8%), we called upper superficial branches. (5) The most frequently observed type of suprascapular artery (Ss) was Type b (38.2%), followed by Type a (25.7%), which branches independently from Su. We concluded that the sites at which Tc and Ss originate are the positions at which they traverse the brachial plexus (superior, transfixed to the plexus). (6) In cases in which the supreme intercostal artery (Is) and the deep cervical artery (Cp) were separate, (Types d-i excluding Type g: 31.9%), Is branched from a more proximal position than Cp.     

A study on the communication between the pectoral nerve and the extramural nerve branches of the intercostal nerves]

Kumaki et al. (1979) defined the extramural nerve as the rudimentary sensory nerve which appeared on the upper thoracic wall; it branched off the root of the lateral cutaneous nerve of the second, third or fourth intercostal nerve, ran inferomedially adhering to the fascia of the intercostalis externus muscle and ended supplying the membrane covering the adjacent rib. They also stated that the extramural nerve (Rxm) occasionally became a cutaneous nerve which pierced the pectoralis muscles and supplied the skin covering the thoracic wall similar to the lateral cutaneous nerve (Rcl) or the anterior cutaneous nerve (Rca). Further, they proposed that the muscular nerves to the obliquus externus abdominis muscle which are usually situated below the fifth rib might be considered a part of this Rxm series. Although the definition of Rxm is still not widely accepted, Rxm is thought to be a key morphological factor influencing the variations of peripheral nerve arrangement on the thoracic wall. In the student course of gross anatomy dissection at Iwate Medical University School of Medicine during the years 1987-1991, three cases of Rxm communicating with the pectoral nerve and supplying the pectoralis major muscle were observed. Some cases have been reported in which Rcl innervates part of the pectoral muscles. However, the communication between the pectoral nerve and Rxm has not yet been discussed. Therefore, to clarify the morphological significance of the communication between Rxm and the pectoral nerve, the branching pattern and the distribution of the pectoral nerves were extensively investigated and the intramuscular nerve supply of some pectoral nerves, especially the pectoral nerves which communicated with Rxm, was examined in detail under a stereomicroscope. The results are summarized as follows: 1. In the first case, Rxm of the second intercostal nerve originated from Rcl, ran inferomedially adhering to the fascia of the intercostalis externus muscle and pierced the origin of the pectoralis minor muscle at the third intercostal space. Then Rxm turned superolaterally to communicate with a pectoral nerve which originated from the loop composed of the lateral and medial pectoral nerves and passed inferior to the pectoralis minor muscle. After communication, the pectoral nerve with Rxm supplied the caudalmost part of the sternocostal portion of the pectoralis major muscle. In the second case, a similar branch of Rxm of the second intercostal nerve passed inferior to the pectoralis minor muscle.(ABSTRACT TRUNCATED AT 400 WORDS)     

Classification system for flexor digitorum accessorius longus muscle variants within the leg: Clinical correlations

The flexor digitorum accessorius longus (FDAL), a variant leg muscle, can cause tarsal tunnel syndrome. This study was performed to classify the variants of the FDAL by dissection and to correlate the dissection results with clinical cases of tarsal tunnel syndrome caused by this muscle. Eighty lower limbs of embalmed Korean cadavers were dissected. MR images of two clinical cases of tarsal tunnel syndrome caused by the FDAL were correlated with the dissection results. The FDAL was observed in nine out of 80 specimens (11.3%) and it was classified into three types depending on its site of origin and its relationship to the posterior tibial neurovascular bundle (PTNV) in the leg. In Type I (6.3%), the FDAL originated in the leg and ran superficially along the PTNV, either not crossing (Type Ia, 3.8%) or crossing (Type Ib, 2.5%) the neurovascular bundle. In Type II (6.3%), it originated in the tarsal tunnel. Most FDALs followed a similar course in the tarsal tunnel and the plantar pedis. On correlating the MR images of the clinical cases with this classification, the FDAL corresponded to Types Ia and II. All three types of FDAL can compress the tibial nerve in the tarsal tunnel or the distal leg. Clarification of the topographical relationship between this muscle and the PTNV would help to improve the results of surgery for tarsal tunnel syndrome caused by the FDAL. Clin. Anat. 27:1111–1116, 2014. © 2014 Wiley Periodicals, Inc.     

Fibularis Tertius: Anatomical Study and Review of the Literature

Although there is much morphological variation in the anterior compartment of the leg, there is little information about the morphological variability of the fibularis tertius muscle (FTM). The main aim of the present study was to characterize the morphology (origin and insertion) and frequency of occurrence of the FTM and to use these findings as the basis for a new classification of the fibularis tertius tendon. Classical anatomical dissection was performed on 106 lower limbs fixed in 10% formalin. The presence of the FTM and the morphology of both its origin and its insertion were described. The FTM was present in 91 limbs (85.8%). Three types of origin were observed: Type 1, the most common type, with its origin on the distal half fibula (67%); Type 2, with the origin on the distal third fibula (22%); and Type 3, with an origin from the tendon of the extensor digitorum longus (11%). In addition, six types of insertion were distinguished. The most common was Type I (45%), a single distal attachment where the tendon inserts into the shaft of the fifth metatarsal bone. The rarest was Type VI, characterized by fusion with an additional band of the fibularis brevis tendon, which gives rise to the fourth interosseus dorsalis muscle. Two morphological variants of insertion could be distinguished, fan‐shaped and band‐shaped. Both the origin and insertion of the FTM are very morphologically variable, with three types of origin (Types 1–3) and six types of insertion point (Types I–VI) observed. Knowledge of such variations is essential for both clinicians and anatomists. Clin. Anat. 32:1082–1093, 2019. © 2019 Wiley Periodicals, Inc.     

Constant existence of the sensory branch of the nerve to the pyramidalis distributing to the upper margin of the pubic ramus

Twenty-one sides of 11 adult Japanese cadavers were investigated, and 2 of 21 sides exhibited absence of the pyramidalis. We observed that all of the nerves to the pyramidalis included the sensory nerve branch, which distributed to the aponeurotic tissue in the upper area of the pubic ramus. To investigate the clinical relevance and developmental process of the pyramidalis, detailed innervation patterns of the pyramidalis and the lumber plexus were examined and compared with the case of absent pyramidalis. The nerves to the pyramidalis could be classified into five types by the derivative nerves and two subtypes by their courses associated with the funiculus spermaticus. In the cases of absent pyramidalis, similar sensory branches distributed close to the upper area of the pubic ramus. We deduced that the sensory branch extended along with the muscular branch to the pyramidalis after development of the pyramidalis and that only the sensory branch remained in cases in which the pyramidalis disappeared. The two subtypes might associate with descensus testis. Surgeons performing inguinal hernia repair using a mesh and tension-free surgical technique should preserve the nerves around the funiculus spermaticus to avoid diminished proprioception in the lower abdominal wall.     

Development of the spinal nerves in the mouse with special reference to innervation of the axial musculature

Development of the mouse spinal nerves was studied. On E11 (11th day of gestation), the primitive spinal nerve fascicle extended ventrally in the anterior half of the sclerotome. Spinal nerves in the forelimb region united with each other to form the primitive brachial plexus. Their terminal segment was covered by a peculiar cell mass. On E12, five primary branches developed along the primitive spinal nerve trunk. The ramus dorsalis was originally a cutaneous nerve, supplying two series of branches to the skin of the back. The medial series was derived from the dorsal ramus of C2–C8, and the lateral series from C8 and the more caudal dorsal rami. Nerves of the former series took the presegmental course through the intermyotomic space, while those of the latter the postsegmental course. The ramus cutaneus lateralis was a nerve that took the presegmental course to become cutaneous. The ramus intercostalis externus was a muscle branch whose distribution was restricted within the segment. The ramus anterior was a muscle branch from the end of the primitive spinal nerve trunk. The ramus visceralis connected a thoracic nerve with the para-aortic sympathetic cell cord. On E13–16 the ramus anterior secondarily gave off a cutaneous branch (ramus cutaneus anterior). The ramus intercostalis externus extended ventrally deep to the intercostalis externus muscle, crossing just caudal to the ramus cutaneus lateralis that secondarily gave off branches to the obliquus externus abdominis muscle.     

The course and variations of the branches of the musculocutaneous nerve in human fetuses

The course and branches of the musculocutaneous nerve (MCN) were dissected in 140 human fetal arms. The MCN entered the superior, middle, and inferior part of coracobrachialis in 43%, 37%, and 17% of arms, respectively, and the remaining 3% did not pierce coracobrachialis. The motor branches to biceps were classified as follows: Type 1 (83.6%): a single branch that bifurcated to supply the two heads of biceps; Type 2 (14.3%): two separate branches each innervating one head of biceps; Type 3 (2.1%): a single branch that bifurcated to supply each head of biceps plus an additional branch that innervated the distal part of biceps. The motor branches to brachialis were classified as follows: Type 1 (93.6%): a single branch to brachialis; Type 2 (6.4%): a single branch that bifurcated into two branches both supplying brachialis. Communications between the MCN and the median nerve (MN) were observed in 10% of specimens, of which three types (A, B, C) could be identified depending on their origin and union. In the most frequently observed type (B, 50% of cases) the communicating branch arose from the proximal part of the MCN and joined the MN in the middle or distal part of arm. The data presented here will be of use to surgeons, especially pediatric surgeons who undertake surgical procedures in the axilla and arm. Clin. Anat. 22:337–345, 2009. © 2008 Wiley‐Liss, Inc.     

The origin of the premotor potential recorded from the second lumbrical

PURPOSE: When recording with a palm electrode, a premotor potential (PMP) precedes the compound muscle action potential evoked from the second lumbrical muscle following median nerve stimulation. The origin of the premotor potential has remained uncertain. The aim of this study was to determine whether the PMP-2L is a SNAP derived from antidromically activated digital sensory branches of the median nerve. METHODS: We recorded three active electrodes were placed over the second lumbrical muscle, the third lumbrical muscle, the fourth lumbrical muscle by multi-channel recordings. RESULTS: PMPs are recorded only over the median digital sensory branches after stimulating the median nerve, while they are recorded only over the ulnar branch after stimulating the ulnar nerve. CONCLUSIONS: We conclude that the origin of the PMP is a SNAP arising from antidromically activated digital sensory branches.     

A supernumerary muscle between the adductors brevis and minimus in humans.

In order to elucidate the nerve supply of a supernumerary muscle observed between the adductors brevis and minimus in humans and to investigate its true nature and mechanism of formation, 100 body halves from 50 adult Japanese cadavers were subjected to gross anatomical examination. A supernumerary muscle was noted in 33 (33.0%) out of the 100 thighs. In each of these thighs, it arose from the upper part of the inferior ramus of the pubis and ran obliquely downwards and laterally. It was inserted into the anterior surface of the insertion aponeurosis of the adductor minimus (17/33 thighs, 51.5%), the upper part of the pectineal line (9/33 thighs, 27.3%), or the posterior side of the base of the lesser trochanter (7/33 thighs, 21.2%). It was supplied, from its posterior aspect, by a filament from the twig originating from the posterior branch of the obturator nerve and being distributed to the superficial fasciculus of the obturator externus (18/33 thighs, 54.5%) or by a twig directly originating from the posterior branch (15/33 thighs, 45.5%). The obturator nerve received fibers from L1234 (4/33 thighs), L234 (25/33 thighs), L2345 (2/33 thighs) or L34 (2/33 thighs) and, moreover, its posterior branch ran through (25/33 thighs, 75.8%) or over (8/33 thighs, 24.3%) the obturator externus to emerge into the thigh. Based on the topographical-anatomical relationships of this muscle to its nerve supply, it seems probable that it is formed by separation from the superficial layer of the obturator externus and changes into an independent structure during the process of ontogeny. Furthermore, from a statistical standpoint, the segmental composition or course of the obturator nerve is not related to either the formation or incidence of this muscle.     

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.     

Radial nerve contribution to brachialis in the UK Caucasian population: position is predictable based on surface landmarks

The midline of the brachialis muscle is now regarded by many surgeons as an internervous plane, between the musculocutaneous nerve supply to the medial portion and a radial nerve contribution to the lateral portion, a principle applied in anterior approaches to the humerus. The radial nerve to brachialis has been described previously in East Asian specimens (Ip and Chang, 1968, Anat Rec 162:363-371; Mahakkanukrauh and Somsarp, 2002, Clin Anat 15:206-209). We sought to investigate the occurrence and character of this nerve in the UK Caucasian population. Dissection of the musculocutaneous nerve and radial nerve was carried out in Caucasian cadaveric arms (n = 42). The radial nerve was dissected from the spiral groove to the lateral epicondyle. Where a branch to brachialis was encountered, its course and level of origin relative to the length of the arm were noted. The musculocutaneous nerve innervated the brachialis in all specimens. Upon investigation 67% of specimens were found to have a radial nerve branch to brachialis. Sixty-one percent of these branches went straight into the muscle, 13% descended, and 26% recurred. The level of origin of the radial nerve branch to brachialis was at a mean of 23% of the distance between the lateral epicondyle and the acromion (n = 31, range 17-37%, SD = 5.3). In three specimens, two branches were observed. A radial nerve contribution to the innervation of the brachialis was present in 67% of UK Caucasian cadavers, which is less than that noted by others in East Asian specimens. The level of the origin of these branches is predictable based on surface landmarks. This fact may be of use during humeral surgery.     

经皮椎弓根螺钉技术的解剖学基础及其临床意义

目的：为经皮椎弓根螺钉技术提供解剖学基础并在此基础上分析经皮植入椎弓根螺钉较常规开放植入椎弓根螺钉临床应用的优点。方法：选用10具经防腐固定，在解剖显微镜下对胸腰段脊柱后部结构进行逐层解剖，重点观测脊神经后支及其分支、脊柱节段动静脉的后支的来源、走行以及分布规律。结果：脊神经后支的内侧支经骨纤维管下行沿途支配横突棘肌，支配下方小关节突、筋膜和韧带。外侧支向外下行走，沿途支配背部深层肌肉。节段动脉的后支在椎间孔的上外方绕向后下方，走行于脊神经的下方和下位脊椎上关节突的外方，分为内外两支穿行于腰部深层肌肉。节段静脉后支与同名动脉伴行，并与对侧、相邻节段同名静脉在棘突和横突部位构成静脉丛。结论：避免损伤脊神经后支和节段动静脉的后支并运用可视化操作系统的经皮椎弓根螺钉植入技术，是微创脊柱外科一种新的技术手段。     

腓骨短肌肌瓣的血供研究与临床应用

目的 了解腓骨短肌血供的解剖学特征,探讨临床应用腓骨短肌肌瓣和以腓骨短肌为蒂的组织瓣内移修复踝周软组织缺损或治疗胫骨骨不连的可行性。 方法 30例经10%福尔马林固定的成人下肢标本,动脉灌注红色乳胶,解剖观察腓骨短肌的血管来源、走行及分布情况;临床上设计切口取腓动脉的弓形动脉分支为蒂,修复踝周软组织缺损和胫骨骨不连患者10例。 结果 腓骨短肌血管呈节段性分布,主要来自腓动脉的弓形动脉,最远侧的分支平均位于外踝上(50.81±5.45) mm;根据腓骨短肌及血供特点,临床设计的腓骨短肌肌瓣应用于10例患者,均获成功。 结论 腓骨短肌血供丰富,逆行腓骨短肌肌瓣血供可靠,是修复踝周软组织缺损和胫骨骨不连的一种理想肌瓣。     

Anatomy of branches of the musculocutaneous nerve to the biceps and brachialis in human fetuses

Forty upper limbs (20 right and 20 left) of spontaneously aborted human fetuses were examined to determine the branching patterns of the musculocutaneous nerve. The mean age of the fetuses was 21.3 weeks. We identified three branching patterns of the musculocutaneous nerve to the biceps muscle. Type I with a single primary branch occurred in 47.5% of cases. Type II with two primary branches each to a separate head of the biceps muscle was observed in 42.5% of cases. Type III consisted of two primary branches, the proximal dividing into two branches, each to a different head of the biceps, and the distal branch supplying the common belly. Type III was present in 10% of cases. We found only one branching pattern for the brachialis muscle, a single primary branch. In our material communicating branches between the median and musculocutaneous nerves were found in 20% of specimens. We measured the distances between the acromion and the exit points of the first and second branch to the biceps, which averaged 36.3% for the first branch regardless of the type of branching pattern, 54.2% for the second branch in Type II, 60.7% for the second branch in Type III and 60.9% for the branch to brachialis, expressed as a percentage of the distance between the acromion and the lateral epicondyle.