Journal of Anatomy最新文献

Study objective: This study aimed to observe and quantitatively analyze the morphology and distribution of uterine nerve fibers using fluorescence micro-optical sectioning tomography (fMOST). The goal was to provide an accurate morphological reference for pathological evaluations of uterine nerves.

Measurements and main results: Using fMOST technique, we observed and analyzed the distribution of nerve fibers within the uterus. Our findings revealed a radial dispersion of nerve fibers radiating from myometrium to endometrium. The cervix uteri region exhibited a high density of nerve fibers, displaying terminations in a flower spray pattern. In contrast, nerve fibers in corpus uteri were comparatively sparse. However, we identified a unique "vine-like" pattern of a single nerve fiber extending from myometrium to endometrial layer in areas with concentrated nerves.

Conclusions: The fMOST technique is able to effectively elucidate the morphology and distribution of uterine nerve fibers. This method enables three-dimensional visualization of nerves in myometrium and offers a novel approach to observe the pathological changes in uterine nerves.

The study aimed to standardize the cryodehydration technique for bovine fetal hearts, focusing on optimizing protocols for each developmental stage to preserve morphological characteristics. We analyzed 29 bovine fetal hearts categorized into early, middle, and late developmental stages. These hearts underwent cryodehydration until a 60%–70% reduction in original fluid volume was achieved. Biometric data were recorded and statistically analyzed using Pearson correlation tests for age versus weight and age versus number of cryodehydration sessions. Morphometric comparisons before and after cryodehydration were performed using paired t-tests. In Group I, hearts exhibited well-defined structures, including the atrium cordis, ventriculus cordis, auricula atrii, aorta, truncus pulmonalis, and ramus coronaries arteria, which were preserved in Groups II and III. Additionally, in Group I the heart had a conical or flat apex cordis, whereas those in Groups II and III had a more pronounced apex. The average number of cryodehydration sessions required was 9.38 (±1.2) days for Group I, 12.37 (±1.4) days for Group II, and 15 days for Group III. A positive correlation was found between age and sample weight, indicating that more developed hearts were heavier. Similarly, there was a positive correlation between gestational age and the number of cryodehydration sessions, suggesting that more advanced stages required more cryodehydration sessions. Paired t-tests demonstrated high statistical significance in the morphometric parameters before and after cryodehydration, indicating a loss of mass during dehydration. However, there was no alteration in the macroscopic structure of the hearts, which remained morphologically preserved. In conclusion, cryodehydration shows promise for preserving and analyzing the external morphological characteristics of bovine fetal cardiac development. It also provides lightweight, odorless, and easy-to-handle specimens ideal for detailed morphological studies and offers a unique perspective for investigating cardiac morphology in biological research contexts.

The ear region has a strong potential for evolutionary studies. While the petrosal bone suffers from ontogeny and allometry, the bony labyrinth provides crucial information for phylogeny. The study of the bony labyrinth itself allowed for argumentation of the early bovid species Eotragus artenensis and Eotragus clavatus being closely related, while a newly described species and genus of early Bovidae from Montréal-du-Gers (France), formerly attributed to Eotragus, clearly belong to another lineage. The morphology of the bony labyrinth of these oldest bovids confirms that Eotragus is a stem Bovidae, while the new Bovidae is more derived. Since the bony labyrinth is a structure that is little affected by ontogeny, allometry, and sexual dimorphism, we propose this structure and its surrounding petrosal bone as the holotype for this new species. This study shows the importance of the ear region in the context of micro- and macro-evolution.

Within Xenarthra (Eocene-Recent), Folivora developed (late Eocene-Recent) a remarkable diversity with respect to ecology and taxonomy over its evolutionary history. Knowledge of the diversity achieved by members of this clade in high-altitude areas of South America (i.e., Altiplano and Puna regions of Peru, Bolivia, and northwestern Argentina) has been improved in recent decades. A particular example involves the late Neogene Mylodontidae Simomylodon uccasamamensis, known mostly from multiple specimens recovered from the Bolivian Altiplano. Although several anatomical descriptions of this ground sloth have been published, almost nothing is known about its ontogenetic development and the associated morphological changes. Here we describe and compare new specimens of S. uccasamamensis from the upper level of the Tafna Formation (Pliocene) in the eastern Puna (ca. 3800 masl), Argentina, representing the southernmost record of this species. The new material is represented by specimens showing different ontogenetic stages, from infant to adult. One subadult specimen reached an estimated body mass of ca. 232 kg. The comparative study of external and internal morphology (the latter obtained from CT scans and radiography) shows remarkable changes in the mandible and molariforms associated with ontogeny; in addition, evidence suggests that the mfs2-3 are the first functional teeth, followed by mf1 and cf1. Based on our body mass estimates (ca. 232 kg.), we inferred an average lifespan of 14 years, 9-month gestation time, and sexual maturation at 4.1 years, quite similar to the values we obtained based on estimated body masses of adult specimens from Bolivia published by previous authors. Along its latitudinal distribution (ca. 14° S-21° S) S. uccasamamensis co-occurred with other ground sloths (e.g., Megatheriinae, Thalassocninae, and Scelidotheriinae), suggesting niche partitioning. The presence of this medium-sized ground sloth is consistent with the similarity between the faunas of eastern Puna and the Bolivian Altiplano during the Pliocene, which is also concordant with what was observed in other clades, such as Rodentia and Notoungulata.

Pinnipeds have long, sensitive, moveable mystacial vibrissae. In other mammals, intrinsic muscles contribute to protracting the vibrissae. However, the mystacial muscles of pinnipeds have not yet been systematically described. Using traditional histological methods provides us with two-dimensional muscle images, but having the ability to visualise these structures in three dimensions would allow for a more comprehensive understanding of pinniped vibrissal anatomy, especially given the challenges posed by their large and extremely curved mystacial pad. We predicted that harbour seals would have large, regular intrinsic muscles due to their well-organised, moveable vibrissae. We adopted diffusible iodine contrast-enhanced computer tomography (diceCT) to describe, for the first time, the three-dimensional architecture of the mystacial vibrissal muscles found in harbour seals. Our observations show that their vibrissae are organised into grids within the mystacial pad. We identified both sling-shaped and oblique intrinsic muscles that connect one vibrissae to the next in the same row. We also identified extrinsic muscles, including the m. nasolabialis, m. maxillolabialis, m. levator nasolabialis and m. orbicularis oris. Contrary to our prediction, the intrinsic muscles were not very large, although they were regularly distributed throughout the pad. Rather, the extrinsic muscles, particularly the m. nasolabialis and m. maxillolabialis were large, deep and well-defined, running throughout the length of the mystacial pad. Therefore, we suggest that these extrinsic muscles, the m. nasolabialis and m. maxillolabialis, are responsible for driving vibrissal protraction underwater. These findings demonstrate the importance of three-dimensional visualisation techniques in advancing our understanding of mystacial anatomy and function in pinnipeds.

When developing, the mandible presents great plasticity and contains condensed mesenchymal cells that develops into Meckel's cartilage, of which the anterior part forms the mandibular symphysis. Mandible human development studies focus on investigating whether the beginning of mandibular fusion in fetal period is related to symphysis ossification and the tensions imposed on it, considering that tongue movements, mouth opening, and closing can be seen in fetuses. This research analyses tissue modifications during human mandibular symphysis growth using light and scanning electron microscopy to relate them to its functional structure. The study sample consisted of 12 human fetuses distributed into two groups: Group I (GI) of 10–14 weeks old and Group II (GII) of 20–24 weeks old. Fragments of mandibular symphysis were removed en bloc together with the surrounding tissues to preserve the relation with adjacent structures. Decalcified specimens were prepared in semi-serial coronal sections 5-μm-thick and stained with hematoxylin and eosin, Masson՚s trichrome, Verhoeff, and Sirius red for histological analysis with light microscopy. Collagen fibers Type I or III and elastic fibers were quantified by volume fraction (Vv). Coronal sections of the GI and GII symphyseal region were submitted to scanning electron microscopy. Comparison between groups used independent t-test. Our study presents the different endochondral ossification stages in the anterior part of Meckel's cartilage in GI. Both groups showed abundantly vascularized mesenchymal tissue with intense cellular activity forming the mandibular symphysis, such as a source of new osteoblasts adjacent to the newly deposited bone matrix. Scanning electron microscopy analysis revealed an invasion of the bony trabecula in the transverse direction from the hemimandible, rectilinear in GI and sinuous in GII due to interdigitating bone process, promoting its ossification. In collagen Vv analysis was verified a prevalence of type I in GII and type III in GI, indicating a proportional relation between maturation and tissue arrangement. Functionally, the collagen and elastic fibers in the mandibular symphysis were arranged in a pantographic network, and the fibrillar interconnectivity clearly contributes to resilience capacity and efficiency of the force transfer. This study inferred the functional significance of the knowledge about the tissue composition of mandibular symphysis, and the importance of this tissue for surrounding structures. The mesenchymal tissue of mandibular symphysis participates in bone growth process, revealing an adaptation mechanism of mandibular symphysis in the fetal period investigated.

In this study, we aimed to achieve three objectives: (1) to precisely characterize the body plans of Elephantidae and other large herbivorous mammals; (2) based on this analysis, to determine whether the body plans of the extinct woolly mammoth (Mammuthus primigenius) and steppe mammoth (M. trogontherii) differ from those of modern-day Elephantidae: the Asian elephant (Elephas maximus), the African bush (Loxodonta africana), and forest (L. cyclotis) elephants; (3) to analyze how the body plans have changed in extant perissodactyls and proboscideans compared with their Paleogene ancestors. To accomplish this, we studied mammoth skeletons from the collections of Russian museums and compared this data with a large number of skeletons of extant elephantids, odd-toed, and even-toed ungulates, as well as their extinct relatives. We showed that three genera of Elephantidae are characterized by a homogeneous body plan, which is markedly different from other large herbivores. Elephantids break the interrelationship, that exists in artiodactyls and perissodactyls, between the total length of the head and neck on one side and the limb's segments on the other. Their limbs are very tall (inferior in this regard among large ungulates only to the giraffe), and, contrary to the other large herbivorous mammals, elongated due to the length of the proximal segments. This allows them to effectively utilize the principle of inverted pendulum (straight-legged walking) in locomotion. The biggest differences in the body plan of mammoths compared with extant elephants are a markedly larger pelvis, elongated fore- and hindlimbs (due to the increased relative length of their proximal segments), and different proportions of the skull. The body plans of plesiomorphic Paleogene proboscideans and perissodactyls differed markedly from their descendants in every body part; these differences are related, on the one hand, to the allometric growth, and on the other hand, to the advancement of the locomotor apparatus in the course of their evolution. The most notable difference in the body plan between Paleogene proboscidean Moeritherium and extant Elephantidae is the ~2-fold increase in relative limb height.

Concomitant with the rupture of the cloacal membrane in the 6th week of development, the intermediate layer of the perineal-skin epithelium thickens. We investigated its distribution and the development of the corresponding subcutaneous compartments in serial sections of female human embryos and foetuses and prepared 3D reconstructions to establish topographic relations. The thick-skin area becomes restricted to the outlets of the genital and intestinal tracts. The clitoris and labia majora become identifiable at ~7 weeks. The mesenchymal mass inside the clitoris soon divides into the glans and the cavernous bodies. The clitoral hood forms between 10 and 14 weeks as a fold of tissue that extends from proximal to distal over the glans. Due to the caudal bending of the clitoral shaft, the labia majora gradually cover the clitoris after ~14 weeks. The labia minora form at ~8 weeks from the ridges of thick-skin epithelium that flank the genital exit. They are continuous ventrolaterally with the clitoral hood and ventromedially with the apex of the cavernous body. Dorsally, their dense subcutaneous mesenchymal core extends to the anal canal. Between 8 and 14 weeks, the urethra lengthens axially, while the vaginal vestibule extends ventrally. In this period, the urethral plate of female embryos is mitotically active but does not increase in volume, which suggests that it contributes to vestibular growth. In conclusion, we observed a temporal correlation between the development of the thick-skin epithelium and that of the external genitals, with a distribution that is reminiscent of the dihydrotestosterone-sensitive skin.

Concomitant with the rupture of the cloacal membrane, the perineal skin epithelium thickens (see accompanying article). In this study, we establish in female embryos and foetuses that the thick skin area divides into ventral and dorsal areas at ~14 weeks and gradually becomes restricted to the vaginal vestibule and anal canal thereafter. The dense mesenchymal core of the labia minora, which forms at ~8 weeks, extends dorsally to the anal canal as a midline reinforcement. The skin epithelium overlying this reinforcement is much thinner than the flanking ‘thick skin’, and is supported by an interrupted basement membrane, which implies epithelial–mesenchymal transformation of the thin midline epithelium and the subsequent establishment of the perineal raphe by the merging of the adjacent thick epithelium. Meanwhile, the anogenital distance in the perineum increases rapidly in length. Perhaps as a consequence, the labia minora cover only the ventral third of the vaginal vestibule at 20 weeks. The endodermal ducts of Bartholin's glands are identifiable at 7 weeks, while acini form at ~12 weeks. The vestibular bulbs become identifiable at ~10 weeks and form vascular networks after ~14.5 weeks. After the rupture of the cloacal membrane, the diameter of the junction of the dorsal cloaca with the anal canal is just a pinhole but widens dorsoventrally after the 7th week. The cutaneous muscles of the perineal area form as a ventrally open U-shaped mesenchymal mass, from which the anal sphincter and bulbospongiosus muscle develop. In conclusion, our findings show that thick skin epithelium persists in the vaginal vestibule and anal canal.

Front cover:

Cover image: see Y. Iwasa et al., ‘Human trapezius muscle development during the early fetal period’, this issue.