Distance between intramuscular nerve and artery in the extraocular muscles: a preliminary immunohistochemical study using elderly human cadavers.

PURPOSE: Extraocular muscles are quite different from skeletal muscles in muscle fiber type and nerve supply; the small motor unit may be the most well known. As the first step to understanding the nerve-artery relationship, in this study we measured the distance from the arteriole (25-50 µm in thickness) to the nerve terminal twigs in extraocular muscles. MATERIALS AND METHODS: With the aid of immunohistochemistry for nerves and arteries, we examined the arteriole-nerve distance at 10-15 sites in each of 68 extraocular muscles obtained from ten elderly cadavers. The oblique sections were nearly tangential to the muscle plate and included both global and orbital aspects of the muscle. RESULTS: In all muscles, the nerve twigs usually took a course parallel to muscle fibers, in contrast to most arterioles that crossed muscles. Possibly due to polyinnervation, an intramuscular nerve plexus was evident in four rectus and two oblique muscles. The arteriole-nerve distance usually ranged from 300 to 400 µm. However, individual differences were more than two times greater in each of seven muscles. Moreover, in each muscle the difference between sites sometimes reached 1 mm or more. The distance was generally shorter in the rectus and oblique muscles than in the levator palpebrae muscle, which reached statistical significance (p < 0.05). CONCLUSIONS: The differences in arteriole-nerve distances between sites within each muscle, between muscles, and between individuals might lead to an individual biological rhythm of fatigue in oculomotor performance.

The Filum Terminale Revisited: A Histological Study in Human Fetuses.

Previous studies have suggested that secondary neurulation provides no functional neurons but only the filum terminale. However, no studies have confirmed that the coccygeal and lower sacral nerves do not originate from the secondary neural tube but only from the primary tube. To obtain a better understanding of these relationships, we examined sagittal or frontal sections from 20 embryonic and fetal specimens ranging from 6 to 14 weeks of gestation. During the growth of the vertebral column as well as the subsequent upward migration of the caudal end of the dural sac, the secondary neural tube was stretched to maintain the original attachment to the coccyx or the lower sacral vertebra. The filum-like structure showed much individual variability but in all cases appeared to be derived from the stretched neural tube. Intermediate age morphology revealed that the secondary neural tube itself provided an initial filum terminale before the ascent of the dural sac. Given that the coccygeal and lower sacral nerves are likely to originate from the secondary neural tube, these parts of the tube persisted and differentiated into spinal neurons to form the anococcygeal nerves. Likewise, the filum terminale was also most likely to contain some neurons that persisted postnatally. Depending on the timing and site of degeneration of the secondary neural tube, individual variations could occur in proportion to the amount of sensory and motor elements in the anococcygeal nerve supply.

Anterior Corticospinal Tract Revisited: A Study Using Human Fetuses.

In the human corticospinal tract (CST), the anterior CST is known to be much thinner than the lateral CST, but fetal development of the CST remains obscure. In this study, we examined horizontal histological sections of the cervical spinal cord from 50 midterm fetuses (crown-rump length, CRL, 70-150 mm; 12-18 weeks) as well as 15 late-stage fetuses (CRL 230-250 mm; 28-30 weeks). While the lateral CST appeared at 14-15 weeks in the cervical cord of the midterm fetuses, we found the anterior CST in only 3 fetuses: CRL 117 mm (15 weeks), and CRL 144 and 150 mm (18 weeks). However, in the late-stage fetuses, the anterior CST exhibited a spectrum of variations, including bilaterally thick tracts (3 fetuses), a unilaterally thick tract (5 fetuses) and a thin or absent tract (7 fetuses). In the group with the thickest anterior CST, the cross-sectional area reached 40% of that of the lateral CST. In contrast to the stable morphology of the lateral CST, the shape of the anterior tract varied slightly between the cervical segments. Immunohistochemical observations demonstrated no difference between the lateral and anterior CSTs: (1) in macrophage infiltration, which suggests apoptosis, and (2) in the arrangement of radial glial fibers. Our findings indicate that the development of the anterior CST starts later than that of the lateral tract, with significant individual variations. The functional relevance of the anterior CST, if present, might not be found in an independent cortical input to motor neurons but in a remodeling of the ascending tracts.

Topographical relationships of intramuscular nerves and vessels of the motor endplates in the thigh and gluteal regions of human fetuses: an immunohistochemical study.

PURPOSE: The aim of this study was to describe topography of vessels and nerves in striated muscles to understand individual muscle function. MATERIALS AND METHODS: Immunohistochemistry for nerve and artery was used to examine the thigh and gluteal muscles of six human midterm fetuses. RESULTS: The supplying nerves often accompanied arteries along epimysium bundling muscle fibers as well as in the covering fascia surrounding the entire muscle mass. However, courses of nerve twigs were usually independent of those of vessels in muscle bundles. Notably, irrespective of whether or not the vascular bundle accompanied the nerves at the muscle surface or hilus, most of the motor endplate bands did not accompany the vessels. CONCLUSION: Since the motor endplates were low vascularised, a chemical induction of vessels for nerve terminal development (or the reversed induction) seemed unlikely in striated muscles. In contrast to proprioceptive neuromuscular facilitation, manual stimulation of the endplate bands may stimulate muscle activity without sympathetic reflexes through vessel-accompanying nerves.

Sensory pathways in the human embryonic spinal accessory nerve with special reference to the associated lower cranial nerve ganglia.

BACKGROUND AND PURPOSE: Muscles supplied by the spinal accessory nerve are particularly prone to the development of trigger points characteristic of myofascial pain. This study aimed to confirm sensory pathways in the spinal accessory nerve and to describe sensory ganglion cell distributions along the lower cranial nerve roots. METHODS: Using sagittal sections of ten human embryos at 6-7 weeks and horizontal sections of three 15- to 16-week-old embryos, we analyzed ganglion cell distributions along the lower cranial nerve roots, including the spinal accessory (XI) nerve. RESULTS: In all ten 6- to 7-week-old embryos, the XI nerve root contained abundant ganglion cells, which were evenly distributed along the XI nerve root at levels between the jugular foramen and the dorsal root of the second cervical nerve. However, the hypoglossal (XII) nerve roots did not contain ganglion cells and did not communicate with nearby roots in the dural space. Thus, the so-called Froriep's occipital ganglion is unlikely to be associated with the XII nerve but rather with the XI nerve roots. According to observations of three larger fetuses (15-16 weeks), most of Froriep's ganglion cells seemed to have degenerated during early fetal life. CONCLUSION: Nociceptive sensory pathways in the adult human XI nerve may be much more limited in number than would be expected based on previous animal studies. However, it is possible that sensory ganglion cells in the embryonic XI nerve root send axons toward the developing spinal accessory nerve fibers outside of the jugular foramen.

Evaluation of road traffic noise abatement by vegetation treatment in a 1:10 urban scale model.

A 1:10 scale of a street canyon and courtyard was constructed to evaluate sound propagation when various vegetation treatments including trees, shrubs, vegetated facades, and green roofs were installed in the urban environment. Noise reductions in the street canyon and courtyard were measured for both single and combined vegetation treatments. Vegetated facades mitigated the overall noise level up to 1.6 dBA in the street canyon, and greening facades were effective to reduce low frequency noise levels below 1 kHz. Trees increased the noise level at high frequency bands to some extent in the street canyon, while the noise level over 1 kHz decreased in the courtyard after installing the street trees. This is because tree crowns diffused and reflected high frequency sounds into the street canyon. Green roofs offered significant noise abatement over 1 kHz in the courtyard, while the vegetated facade was effective to reduce noise levels at low frequencies. In terms of the integrated effects of vegetation treatments, a combined vegetation treatment was less effective than the sum of single treatments in the street canyon. The maximum noise reduction observed for all combinations of vegetation treatments provided 3.4 dBA of insertion loss in the courtyard.

Speech privacy and annoyance considerations in the acoustic environment of passenger cars of high-speed trains.

It is necessary to consider not only annoyance of interior noises but also speech privacy to achieve acoustic comfort in a passenger car of a high-speed train because speech from other passengers can be annoying. This study aimed to explore an optimal acoustic environment to satisfy speech privacy and reduce annoyance in a passenger car. Two experiments were conducted using speech sources and compartment noise of a high speed train with varying speech-to-noise ratios (SNRA) and background noise levels (BNL). Speech intelligibility was tested in experiment I, and in experiment II, perceived speech privacy, annoyance, and acoustic comfort of combined sounds with speech and background noise were assessed. The results show that speech privacy and annoyance were significantly influenced by the SNRA. In particular, the acoustic comfort was evaluated as acceptable when the SNRA was less than -6 dB for both speech privacy and noise annoyance. In addition, annoyance increased significantly as the BNL exceeded 63 dBA, whereas the effect of the background-noise level on the speech privacy was not significant. These findings suggest that an optimal level of interior noise in a passenger car might exist between 59 and 63 dBA, taking normal speech levels into account.

Influence of wall scattering on the early fine structures of measured room impulse responses.

The effects of wall diffusing elements on sound-field diffuseness were investigated in a tenth-scale model hall and in a real recital hall. Acoustical measurements were carried out in both halls to measure the surface diffusivity of the lateral walls. In the scale model, the surfaces of the lateral walls and the soffits were covered with diffusers; in the recital hall, the front halves of both lateral walls were treated using reflective panels and absorptive materials. Objective characteristics were investigated using conventional room acoustic parameters and the number of peaks (Np) computed for the measured impulse responses, which were recorded under diffusive, reflective, and absorptive conditions. In addition, as a measure of the diffuse sound fields, the relative standard deviations (RSDs) of the acoustical parameters were investigated. The diffusive surfaces caused a decrease in the standard deviation of the early decay time and an increase in the Np at higher frequency bands. Auditory experiments using a paired comparison method revealed that the perception of subjective diffuseness could be quantified by using Np. In addition, one listener group's preference was correlated with Np and varied depending on different wall surface treatments.

The habenulo-interpeduncular and mammillothalamic tracts: early developed fiber tracts in the human fetal diencephalon.

PURPOSE: The habenulo-interpeduncular (HI) and mammillothalamic (MT) tracts are phylogenetically ancient. The clinical relevance of these tracts has recently received attention. In this work, we map the anatomy the developing HI and MT. METHODS: To investigate the topographical anatomy of developing fiber tracts in and around the diencephalon, we examined the horizontal, frontal, and sagittal serial paraffin sections of 28 human fetuses at 8-12 weeks of gestation. RESULTS: In all specimens, eosinophilic early fiber bundles were limited to the bilateral HI and MT tracts in contrast to pale-colored later developing fibers such as the thalamocortical projections and optic tract. The HI and MT tracts ran nearly parallel and sandwiched the thalamus from the dorsal and ventral sides, respectively. The nerve tract course appeared to range from 5-7 mm for the HI tract and 3-5 mm for the MT tract in 15 specimens at 11-12 weeks. The HI tract was embedded in, adjacent to, or distant from the developing parvocellular red nucleus. CONCLUSIONS: In early human fetuses, HI and MT tracts might be limited pathways for primitive cholinergic fiber connections between the ventral midbrain and epithalamic limbic system.

The role of diffusive architectural surfaces on auditory spatial discrimination in performance venues.

In musical or theatrical performance, some venues allow listeners to individually localize and segregate individual performers, while others produce a well blended ensemble sound. The room acoustic conditions that make this possible, and the psycho-acoustic effects at work are not fully understood. This research utilizes auralizations from measured and simulated performance venues to investigate spatial discrimination of multiple acoustic sources in rooms. Signals were generated from measurements taken in a small theater, and listeners in the audience area were asked to distinguish pairs of speech sources on stage with various spatial separations. This experiment was repeated with the proscenium splay walls treated to be flat, diffusive, or absorptive. Similar experiments were conducted in a simulated hall, utilizing 11 early reflections with various characteristics, and measured late reverberation. The experiments reveal that discriminating the lateral arrangement of two sources is possible at narrower separation angles when reflections come from flat or absorptive rather than diffusive surfaces.

Comparative Spatial Transcriptomic and Single-Cell Analyses of Human Nail Units and Hair Follicles Show Transcriptional Similarities between the Onychodermis and Follicular Dermal Papilla.

The nail unit and hair follicle are both hard keratin-producing organs that share various biological features. In this study, we used digital spatial profiling and single-cell RNA sequencing to define a spatially resolved expression profile of the human nail unit and hair follicle. Our approach showed the presence of a nail-specific mesenchymal population called onychofibroblasts within the onychodermis. Onychodermis and follicular dermal papilla both expressed Wnt and bone morphogenetic protein signaling molecules. In addition, nail matrix epithelium and hair matrix showed very similar expressions profile, including the expression of hard keratins and HOXC13, a transcriptional regulator of the hair shaft. Integration of single-cell RNA sequencing and digital spatial profiling data through computational deconvolution methods estimated epithelial and mesenchymal cell abundance in the nail- and hair-specific regions of interest and revealed close transcriptional similarity between these major skin appendages. To analyze the function of bone morphogenetic proteins in nail differentiation, we treated cultured human nail matrix keratinocytes with BMP5, which are highly expressed by onychofibroblasts. We observed increased expressions of hard keratin and its regulator genes such as HOXC13. Collectively, our data suggest that onychodermis is the counterpart of dermal papilla and that BMP5 in onychofibroblasts plays a key role in the differentiation of nail matrix keratinocytes.

Single-cell RNA sequencing of human nail unit defines RSPO4 onychofibroblasts and SPINK6 nail epithelium.

Research on human nail tissue has been limited by the restricted access to fresh specimen. Here, we studied transcriptome profiles of human nail units using polydactyly specimens. Single-cell RNAseq with 11,541 cells from 4 extra digits revealed nail-specific mesenchymal and epithelial cell populations, characterized by RSPO4 (major gene in congenital anonychia) and SPINK6, respectively. In situ RNA hybridization demonstrated the localization of RSPO4, MSX1 and WIF1 in onychofibroblasts suggesting the activation of WNT signaling. BMP-5 was also expressed in onychofibroblasts implicating the contribution of BMP signaling. SPINK6 expression distinguished the nail-specific keratinocytes from epidermal keratinocytes. RSPO4+ onychofibroblasts were distributed at close proximity with LGR6+ nail matrix, leading to WNT/ß-catenin activation. In addition, we demonstrated RSPO4 was overexpressed in the fibroblasts of onychomatricoma and LGR6 was highly expressed at the basal layer of the overlying epithelial component, suggesting that onychofibroblasts may play an important role in the pathogenesis of onychomatricoma.

Effects of curcumin for preventing restenosis in a hypercholesterolemic rabbit iliac artery stent model.

OBJECTIVE: To evaluate the efficacy of the curcumin-coating stent (CCS) on the inhibition of restenosis in a rabbit iliac artery stent model. RESULTS: Curcumin, pigment naturally acquired from the rhizome of the plant curcuma longa, is known to have antiproliferative, antimigratory, and anti-inflammatory effects. However, it is still unclear that curcumin can inhibit neointimal proliferation of the injured vessel. METHODS: Dose-dependent inhibition of cell growth was observed over a dose range from 10 nM to 10 microM. CCS was prepared by a dip-coating method (high-dose: HD, low-dose: LD). The release profile of the HD CCS showed that drug release persisted until day 21. Scanning electron microscopy of the CCS showed an intact surface of the stent even after expansion. To test the efficacy of CCS in vivo, LD CCS, HD CCS, and bare metal stents (BMS) were implanted in random order in one iliac artery (N = 30 arteries) of male New Zealand White rabbits (N = 15). RESULTS: After 28 days, the LD and HD CCS groups had a 43% and 55% reduction in the neointimal area, compared with the BMS group (BMS 3.3 +/- 1.0 mm(2), LD 1.9 +/- 0.8 mm(2), and HD 0.9 +/- 0.5 mm(2), P < 0.05). There appeared to be no cytotoxicity related to curcumin at the indicated doses. CONCLUSIONS: Curcumin, a natural compound in the human diet, seems to be a safe and effective candidate drug for use in a drug-eluting stent for the prevention of stent restenosis following angioplasty.

Fetal Development of Fasciae around the Arm and Thigh Muscles: A Study Using Late Stage Fetuses.

To obtain a better understanding of multi-laminar deep fascia covering skeletal muscles, we examined nondecalcified histological sections of the arm and thigh of 20 human fetuses aged 25-33 weeks. Morphologies of the fasciae varied between sites and specimens, but the initial morphology was most likely to be a thin and loose sheet on the external surface of the muscles (fascia-1 or F1). When the F1 became wavy, thick and tight, it was detached from the muscle surface. Beneath the F1, the second lamina of fascia (F2) appeared on the muscle surface and it was also detached. In this manner at 25-33 weeks' gestation, fasciae covering the triceps and vastus lateralis muscles had a three-layered configuration (F1, F2, and F3). Due to significant individual variations, this process was not correlated to the ages and sizes of specimens. Muscle contractions might facilitate the detachment. In these muscles, the intramuscular tendon joined the F2 or F3 and the latter became thick and aponeurotic. Along the finally developed lamina, muscle fibers carried a desmin-positive spot for insertion. Increased laminae were accompanied by a reduced number of CD68-positive macrophages and, nerves were absent, near the developing fascia. In contrast to skin ligaments or superficial fasciae showing de novo development in loose tissue, a deep or muscle-covering fascia seemed to originate from the skeletal muscle itself at the surface, and this process was repeated to produce multi-layered fascia. Depending on sites, collagen fibers were added by the intramuscular tendon. Anat Rec, 301:1235-1243, 2018. © 2018 Wiley Periodicals, Inc.

Long-term and sustained COMP-Ang1 induces long-lasting vascular enlargement and enhanced blood flow.

Vascular enlargement is a characteristic feature of angiopoietin-1 (Ang1)-induced changes in adult blood vessels. However, it is unknown whether tissues having Ang1-mediated vascular enlargement have more blood flow or whether the enlargement is reversible. We have recently created a soluble, stable and potent Ang1 variant, COMP-Ang1. In the present study, we investigated the effects of varied dose and duration of COMP-Ang1 on vascular enlargement and blood flow in the tracheal microvasculature of adult mice and explored a possible mechanism of long-lasting vascular enlargement. We found that COMP-Ang1 administered by adenoviral vector induced long-lasting vascular enlargement and increased tracheal blood flow. In contrast, short-term administration of COMP-Ang1 recombinant protein induced transient vascular enlargement that spontaneously reversed within a month. In both cases, the vascular enlargement resulted from endothelial proliferation. The COMP-Ang1-induced vascular remodeling is mediated mainly through Tie2 activation. Sustained overexpression of Tie2 could participate in the maintenance of vascular changes. Together, our findings indicate that sustained treatment with COMP-Ang1 can produce long-lasting vascular enlargement and increased blood flow.

Coccygeal body revisited: An immunohistochemical study using donated elderly cadavers.

To describe the normal anatomy and histology of the adult coccygeal body (CB) and to discuss about the origin and function, using immunohistochemistry, we examined 29 CBs found in 32 elderly donated cadavers without macroscopic pathology in the pelvis. The CB was usually located in or near the anococcygeal ligaments. It was almost always composed of multiple masses or nodules of round glomus cells (smooth muscle actin or SMA++). However, the CB sometimes contained abundant dilated veins with scattered glomus cells. Thus, the CBs varied from the glomus cell nodule-dominant type, through an intermediate morphology with a mixture of nodules and veins, to the vein-dominant type. Each glomus cell mass was surrounded by abundant sympathetic nerves. In all specimens, we found multiple abnormal arteries, each of which carried a glomus-like cell layer around the almost -obliterated vascular lumen; as well as an SMA-negative thick arterial wall containing abundant sympathetic nerves. The ligaments around the CB are known to be under strong mechanical stress from the pelvic floor. We considered abnormal arteries containing the unique internal layer as an intermediate between a normal muscular artery and a glomus cell mass of CB. Under long-termed mechanical stress, a muscular artery seems to lose smooth muscles with increased sympathetic nerve fibers, to compensate for the lack of muscle function. Taken together with fetal morphology (our recent report), some or most of the CBs might not be an arteriovenous shunt but a result of stress-induced acquired transformation of pericytes. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 300:1826-1837, 2017. © 2017 Wiley Periodicals, Inc.

[The Influence of Subjective Health Status, Post-Traumatic Growth, and Social Support on Successful Aging in Middle-Aged Women].

PURPOSE: This study was done to investigate factors influencing successful aging in middle-aged women. METHODS: A convenience sample of 103 middle-aged women was selected from the community. Data were collected using a structured questionnaire and analyzed using descriptive statistics, two-sample t-test, one-way ANOVA, Kruskal Wallis test, Pearson correlations, Spearman correlations and multiple regression analysis with the SPSS/WIN 22.0 program. RESULTS: Results of regression analysis showed that significant factors influencing successful aging were post-traumatic growth and social support. This regression model explained 48% of the variance in successful aging. CONCLUSION: Findings show that the concept 'post-traumatic growth' is an important factor influencing successful aging in middle-aged women. In addition, social support from friends/co-workers had greater influence on successful aging than social support from family. Thus, we need to consider the positive impact of post-traumatic growth and increase the chances of social participation in a successful aging program for middle-aged women.

Human nasociliary nerve with special reference to its unique parasympathetic cutaneous innervation.

The frontal nerve is characterized by its great content of sympathetic nerve fibers in contrast to cutaneous branches of the maxillary and mandibular nerves. However, we needed to add information about composite fibers of cutaneous branches of the nasociliary nerve. Using cadaveric specimens from 20 donated cadavers (mean age, 85), we performed immunohistochemistry of tyrosine hydroxylase (TH), neuronal nitric oxide synthase (nNOS), and vasoactive intestinal polypeptide (VIP). The nasocilliary nerve contained abundant nNOS-positive fibers in contrast to few TH- and VIP-positive fibers. The short ciliary nerves also contained nNOS-positive fibers, but TH-positive fibers were more numerous than nNOS-positive ones. Parasympathetic innervation to the sweat gland is well known, but the original nerve course seemed not to be demonstrated yet. The present study may be the first report on a skin nerve containing abundant nNOS-positive fibers. The unique parasympathetic contents in the nasocilliary nerve seemed to supply the forehead sweat glands as well as glands in the eyelid and nasal epithelium.

Significant Differences in Sympathetic Nerve Fiber Density Among the Facial Skin Nerves: A Histologic Study Using Human Cadaveric Specimens.

Sympathetic nerve fibers in the skin nerves are connected with vasomotor, thermoregulatory, sensory input modulatory, and immunologic events; however, to our knowledge, no histological information is available for skin nerves in the human face. Using specimens from 17 donated cadavers (mean age, 86 years), we measured a sectional area of tyrosine hydroxylase (TH)-positive fibers in (1) the frontal nerve (V1), (2) the infraorbital nerve (V2), (3) the mental nerve (V3), (4) the greater auricular nerve (C2), (5) the auriculotemporal nerve (ATN), and (6) the zygomatic branch of the facial nerve (VII). The V1, V2, and V3 were obtained at their entrances to the subcutaneous tissue from the bony canal or notch. The V1, C2, ATN, and/or VII usually contained abundant TH-positive fibers (almost 3%-8% of the nerve sectional area), whereas the V2 and V3 consistently carried few TH-positive fibers (<1%). The difference between these two groups was quite significant (P < 0.001). Thus, from the superior cervical ganglion, the sympathetic nerve fibers reached the forehead through the frontal nerve trunk, whereas artery-bounded fibers came to the cheek, nose, and mouth. The sympathetic palsy caused by trigeminal nerve involvement is mainly characterized by the symptoms seen in the distribution of the ophthalmic division of the trigeminal nerve, such as in Horner's syndrome. It suggests that the forehead and the other facial areas are representative parts of those different sympathetic innervations that could be useful for evaluating the sympathetic function of the face in various diseases. Anat Rec, 299:1054-1059, 2016. © 2016 Wiley Periodicals, Inc.

Median Sacral Artery, Sympathetic Nerves, and the Coccygeal Body: A Study Using Serial Sections of Human Embryos and Fetuses.

To examine how the median sacral artery (MSA) is involved with the coccygeal body or glomus coccygeum, we studied serial frontal or sagittal sections of 14 embryos (approximately 5-6 weeks of gestation) and 12 fetuses (10-18 weeks). At five weeks, the caudal end of the dorsal aorta (i.e., MSA) accompanied putative sympathetic ganglion cells in front of the upper coccygeal and lower sacral vertebrae. At six weeks, a candidate for the initial coccygeal body was identified as a longitudinal arterial plexus involving nerve fibers and sympathetic ganglion cells between arteries. At 10-18 weeks, the MSA exhibited a highly tortuous course at the lower sacral and coccygeal levels, and was attached to and surrounded by veins, nerve fibers, and sympathetic ganglion cells near and between the bilateral origins of the levator ani muscle. Immunohistochemistry demonstrated expression of tyrosine hydroxylase and chromogranin A in the nerves. However, throughout the stages examined, we found no evidence suggestive of an arteriovenous anastomosis, such as well-developed smooth muscle. An acute anterior flexure of the vertebrae at the lower sacrum, as well as regression of the secondary neural tube, seemed to induce arterial plexus formation from an initial straight MSA. Nerves and ganglion cells were likely to be secondarily involved with the plexus because of the close topographical relationship. However, these nerves might play a major role in the extreme change into adult morphology. An arteriovenous anastomosis along the MSA might be an overinterpretation, at least in the prenatal human. Anat Rec, 299:819-827, 2016. © 2016 Wiley Periodicals, Inc.