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Background: During the expansion of the pleural cavity in early fetuses, a thick sheet of loose mesenchymal tissue (SLMT) appears between the lung bud and body wall. Subsequently, the growing lung bud invades into the SLMT and the latter becomes fragmented to disappear. To compare this with the tympanic cavity filled with loose mesenchymal tissues, the present study aimed to demonstrate the development, establishment, and breaking of the SLMT in the retrosternal space. Materials and methods: Although the retrosternal tissue was almost absent or very thin at 7 weeks, the SLMT appeared behind the manubrium sterni at 8 weeks. Accordingly, at 9–10 weeks, cavitation occurred in the SLMT to expand the pleural cavity. Therefore, the volume of SLMT was not determined by the adjacent structures such as the pericardium and sternum. Likewise, mesenchymal tissues filling the middle ear disappeared after 26 weeks. Results: There were considerable individual variations in the timing of beginning and location of the tympanic cavitation. However, in contrast to the retrosternal SLMT, the volume of the future tympanic cavity is determined by the adjacent hard tissue and tympanic membrane much earlier than the cavitation. The mesenchymal tissue carried abundant vessels in the middle ear but none or few veins in the retrosternal SLMT. Conclusions: The concept that the lung bud invades into the splanchnic mesoderm to expand the pleural cavity seems oversimplified. Mechanical stresses from the pleural cavity might induce retrosternal cavitation, while a loss in blood supply might cause tympanic cavitation. [ABSTRACT FROM AUTHOR]

Background and Materials and Methods: To provide better understanding of frequent variations of the inferior oblique (IO) of adult extraocular muscles, we observed sagittal and horizontal histological sections of the eye and orbits from 32 foetuses (7-34 weeks of gestational age; 24-295 mm of crown-rump length).Results: In early foetuses (7-8 weeks), the IO was restricted at an antero-infero-medial angle of the future orbit. In contrast to extraocular recti, the IO appeared to extend along the mediolateral axis and had no definite tendon. At midterm, the IO tendon became evident. Sometimes, the IO muscle belly attached to the inferior rectus or, the IO tendon divided into two laminae to enclose the lateral rectus. At late-term, a multilayered sheath was evident around the sclera and, via one or some of the fascial layers, the IO was communicated with a fascia enclosing the inferior rectus. At midterm and late-term, the IO originated not only from the maxilla near the orbicularis oculi origin but also from a vein-rich fibrous tissue around the lacrimal sac. Both origins were muscular without intermittent tendon or ligament. Therefore, the fascial connection as well as a direct contact between the IO and the inferior or lateral rectus seemed to provide variant muscular bridges as reported in adults. Moreover, the two attachment sites at the origin seemed to provide double muscle bellies of the adult IO.Conclusions: Consequently, the present specimens contained seeds of any types of adult variations. The muscle fibres from the lacrimal sac might play a role for the lacrimal drainage. [ABSTRACT FROM AUTHOR]

Background: The paratenon is a sheath-like connective tissue that allows the tendon to move with minimal friction. The careful removal of the paratenon along the cruciate ligaments is a critical step of knee surgery. Thus, orthopaedic surgeons and interventional radiologists consider the paratenon as a basic anatomical tissue along a ligament, not along a tendon.Materials and Methods: We performed macroscopic and histological observations of cruciate ligament-associated paratenons in 43 human foetuses.Results: This tissue usually had a thick armour-like appearance that was distant from the infrapatellar fat pad. The anterior cruciate ligament, rather than the posterior ligament, was deeply embedded in the paratenon. The paratenon contained abundant arteries and veins and, at and near the crossing between the cruciate ligaments, had a well-developed venous plexus. Notably, there were abundant fused veins in the paratenon venous plexus, and prenatal knee movements (especially rotation) seemed to restrict its blood supply, leading to the development of a large cavity by way of advancing fusion of veins in the degenerating plexus. This unique manner of cavitation likely expanded the joint cavity.Conclusions: Differences in knee movements in utero seemed to cause differences in the thickness of the paratenon among foetuses. New-borns might have limited knee flexion due to a mass-effect of the thick paratenon around the cruciate ligaments. A slight twisting or rotation at the knee may help to release the knee, because it can break the foetal paratenon and accelerate cavitation. [ABSTRACT FROM AUTHOR]

Background: At birth, the ductus arteriosus (DA) merges with the aortic arch in the slightly caudal side of the origin of the left subclavian artery (SCA). Since the SCAs (7th segmental arteries) were fixed on the level of the 7th cervical-first thoracic vertebral bodies, the confluence of DA should migrate caudally. We aimed to describe timing and sequence of the topographical change using serial sagittal sections of 36 human embryos and foetuses (CRL 8-64 mm; 5-10 weeks), Those made easy evaluation of the vertebral levels possible in a few section.Materials and Methods: The DA or 6th pharyngeal arch artery seemed to slide down in front of the sympathetic nerve trunk along 1.0-1.2 mm from the second cervical vertebral level at 5-6 weeks and, at 6 weeks (CRL 14-17 mm), the DA confluence with aorta reached the 7th cervical level. Because of the highly elongated common carotid artery, the sliding of DA confluence seemed to be much shorter than the cervical vertebrae growing from 1 mm to 2.4 mm.Results: At the final topographical change at 6-7 weeks, the DA confluence further descended to a site 1-vertebral length below the left SCA origin. From 6 to 9 weeks, a distance from the top of the aortic arch to the left SCA origin was almost stable: 0.3-0.5 mm at 6 weeks and 0.4-0.6 mm at 9 weeks.Conclusions: The heart descent and the caudal extension of the trachea and bronchi, those occurred before the DA sliding, were likely to be a major driving force for the sliding. [ABSTRACT FROM AUTHOR]

Background: Prenatal twisting of the femoral neck seems to result in an angle of anteversion or torsion, but the underlying process has not been elucidated.Materials and Methods: This study analysed sagittal, frontal and horizontal sections of 34 embryo and foetal specimens of gestational age (GA) 6-16 weeks (crown-rump length 21-130 mm). At GA 6-7 weeks, the iliopsoas (IP) and gluteus medius (GME) muscles were inserted into the anterior and posterior aspects of the femur, respectively, allowing both insertions to be viewed in a single sagittal section.Results: At GA 8 weeks, the greater trochanter and the femoral neck angle became evident, and the GME tendon was inserted into the upper tip of the trochanter. At GA 9 weeks, the location of IP insertion was to the medial side of the GME insertion. After 9 weeks, the IP insertion consisted of a wavy, tendino- us part of the psoas muscle and another part of the iliacus muscle, with many fibres of the latter muscle attached to the joint capsule. After GA 12 weeks, the IP was inserted into the anteromedial side of the greater trochanter, while the aponeurotic insertion of the GME wrapped around the trochanter. At GA 15-16 weeks, a deep flexion at the hip joint caused an alteration in the relative heights of the lesser and greater trochanter, with the former migrating from the inferior to the slightly superior side.Conclusions: These findings indicate that twisting of the femoral neck started at GA 8-9 weeks. [ABSTRACT FROM AUTHOR]

Background: The human tensor fasciae latae muscle (TFL) is inserted into the iliotibial tract and plays a critical role in lateral stabilisation of the hip joint. We previously described a candidate of the initial iliotibial tract that originated from the gluteus maximus muscle and extended distally.Materials and Methods: This study extended our observations by examining 30 human embryos and foetuses of gestational age (GA) 7-14 weeks (crown-to-rump length 24-108 mm). At GA 7 weeks, the TFL appeared as a small muscle mass floating in the subcutaneous tissue near the origins of the gluteus medius and rectus femoris muscles.Results: Subsequently, the TFL obtained an iliac origin adjacent to the rectus femoris tendon, but the distal end remained a tiny fibrous mass on the vastus lateralis muscle. Until GA 10 weeks, the TFL muscle fibres were inserted into a vastus lateralis fascia that joined the quadriceps tendon distally. The next stage consisted of the TFL muscle belly "connecting" the vastus fascia and the gluteus fascia, including our previous candidate of the initial iliotibial tract. Until GA 14 weeks, the TFL was sandwiched by two laminae of the connecting fascia.Conclusions: These findings suggested that, when the vastus lateralis fascia separated from the quadriceps tendon to attach to the tibia, possibly after birth, the resulting iliotibial tract would consist of a continuous longitudinal band from the gluteus maximus fascia, via the vastus fascia, to the tibia. Although it is a small muscle, the foetal TFL plays a critical role in the development of the iliotibial tract. [ABSTRACT FROM AUTHOR]

The digastricus and omohyoideus muscles are digastric muscles with two muscle bellies. An insertion tendon of the posterior belly becomes an intermediate tendon in digastricus muscles, whereas a single band-like muscle in omohyoideus muscles may later be interrupted by an intermediate tendon, possibly due to muscle cell death caused by mechanical stress. In human foetuses, an intermediate tendon provides the temporal origins of the tensor veli palatini and tensor tympani muscles. Some reptiles, including snakes, carry multiple series of digastric-like axial muscles, in which each intersegmental septum is likely to become an intermediate tendon. These findings indicate that many pathways are involved in the development of digastric muscles. A review of these morphologies suggested that the flexor digi-torum superficialis (FDS) muscle was a digastric muscle, although the intermediate tendon may not be visible in the surface view in adults. The present observations support the hypothesis that the proximal anlage at the elbow develops into a deep muscle slip to a limited finger, while the distal anlage at the wrist develops into the other slips. The findings suggest that, in the FDS muscle, the proximal and distal bellies of the embryonic digastric muscle fuse together to form a laminar structure, in which muscle slips accumulate from the palmar to the deep side of the forearm. (Folia Morphol 2018; 77, 2: 362-370). [ABSTRACT FROM AUTHOR]

Development of a long muscle belly in foetal extremities generally requires a definite bony insertion of the long tendon. However, in adults, the pes anserinus and the semimembranosus tendon (SMT) are inserted into fasciae. Development of fascial insertions in foetuses was investigated by examining serial histological sections obtained from 7 foetuses at 8-9 weeks and 8 foetuses at 14-16 weeks. The presence of matrix substances and macrophages was also examined by immunohistochemistry. At 8 weeks, the tendons of the semitendinosus, gracilis, sartorius and semimembranosus muscles were straight and inserted into the initial shaft-like proximal end of the tibia on the proximal side of the popliteus muscle. At 9 weeks, however, the medially extending popliteus muscle appeared to push the pes anserinus tendons superficially, with a loss of cartilage insertions. The SMT obtained an attachment to the popliteus muscle. At 14-16 weeks, the SMT divided into thick and thin bundles: the former contained abundant macrophages and inserted into the tenascin-positive perichondrium of the enlarged proximal tibia, while the later without macrophages ended at the joint capsule. The pes anserinus tendons, negative for both versican and tenascin-c, took highly tortuous courses toward the fascia cruris. Because the medial extension of the popliteus muscle was associated with the enlargement of the proximal tibia, the topographical relationship of the popliteus muscle with these 4 tendons changed drastically, resulting in a loss of cartilage insertion of the pes anserinus tendons as well as the division and reconstruction of the SMT. [ABSTRACT FROM AUTHOR]

Ligament of Henle is one of muscle-associated connective tissues of the rectus abdominis muscle, but it has been confused with the conjoint tendon (a common aponeurosis for insertion of the inferomedial end of the obliquus internus and transversus abdominis muscles). To reconsider the inguinal connective tissue structures, we examined 20 mid-term foetuses (10 males and 10 females) at approximately 14-20 weeks of gestation (crown rump length 100-170 mm). In female horizontal sections, we consistently found the ligament of Henle as a wing-like aponeurosis extending from the lateral margin of the rectus tendon behind the superficial inguinal ring. The ligament was separated from and located behind the conjoint tendon. In all male foetuses, instead of the ligament, the conjoint tendon was evident behind the superficial ring and it winded around the posterior aspect of the spermatic cord. Therefore, although a limited number of specimens were examined, the ligament of Henle was likely to be a female-specific structure. The ligament of Henle, if developed well, may provide an arch-like structure suitable for a name "falx inguinalis" instead of the inferomedial end of the conjoint tendon. In addition, a covering fascia of the iliopsoas muscle joined the posterior wall of the inguinal canal in male, but not in female, specimens. [ABSTRACT FROM AUTHOR]

Birds and reptiles always carry a long and thick artery accompanying the sciatic nerve (i.e. the sciatic artery) whereas mammals do not. We attempted to demonstrate a difference in courses of the nerve and the arteries of foetuses in relation to hip joint posture. Eight mid-term human foetuses (15-18 weeks), five mouse foetuses (E18), and five chick embryos (11 days after incubation) were examined histologically. Thin feeding arteries in the sciatic nerve were consistently observed in human foetuses in spite of the long, inferiorly curved course of the nerve around the ischium. The tissue around the human sciatic nerve was not so tight because of the medial and inferior shift of the nerve away from the hip joint. The foetal hip joint position differed among the species, being highly flexed in humans and almost at right angle flexion in mice and chicks. Because of deep adduction of the hip joint in the mouse, the knee was located near the midline of the body. The mouse sciatic nerve ran through the tight tissue along the head of the femur, whereas the chick nerve ran through the loose space even in the gluteal region. In birds, evolution of the pelvis including the hip joint without adduction seemed to make the arterial development possible. In mammals, highly flexed or adducted hip joint seemed to be one of the disturbing factors against development of the long and thick artery. A slight change in posture may cause significant arterial variation. [ABSTRACT FROM AUTHOR]

A study was conducted, on 30 human fetuses, of the structures passing through the tympanosquamosal fissure. The tympanosquamosal fissure lies between the middle ear and the temporomandibular region. Meckel's cartilage passes through the tympanosquamosal fissure and continues on into the middle ear with the cartilaginous anlage of the malleus. A tract of fibrous tissue arises from the mesenchyme, located cranial and lateral to Meckel's cartilage, that enters from the posterior area of The temporomandibular joint disc to the middle ear through the tympanosquamosal fissure, and attaches onto the area of continuity of Meckel's cartilage with the malleus. Transformation of Meckel's cartilage into the sphenomandibular ligament and anterior ligament of the malleus determines their continuity through the tympanosquamosal fissure. The posterior fibers of the temporomandibular joint disc giving rise to the discomalleolar ligament insert into the anterior ligament of the malleus. [ABSTRACT FROM AUTHOR]

The objective was to study the morphology of the articular disc and analyse the immunohistochemical expression of types I and III collagen markers in the temporomandibular joint (TMJ) disc of human foetuses of different gestational ages. Twenty TMJ from human foetuses supplied by Universidade Federal de Uberaba with gestational ages from 17 to 24 weeks were studied. The gestational age of the foetuses was determined by measuring the crown-rump (CR) length. Macroscopically, the foetuses were fixed in 10% formalin solution and dissected by removing the skin and subcutaneous tissue and exposing the deep structures. Immunohistochemical markers of type I and III were used to characterize the existence of collagen fibres. Analysis of the immunohistochemical markers of types I and III collagen revealed the presence of heterotypical fibril networks.

The objective was to analyze the development of the stapedius muscle to understand an isolated unilateral absence of the tendon of the stapedius muscle in a human fetus. The study was made on 50 human embryos and fetuses aged 38 days to 17 weeks post-conception. The stapedius muscle was formed by two anlagen, one for the tendon, which derives from the internal segment of the interhyale and another for the belly, located in the second pharyngeal arch, medially to the facial nerve and near the interhyale. In the interhyale, two segments were observed forming an angle and delimited by the attachment of the belly of the stapedius muscle. The internal segment will form the tendon. The lateral segment of the interhyale was attached to the cranial end of the Reichert's cartilage (laterohyale), and normally it disappears at the beginning of the fetal period. The right unilateral agenesia of the tendon of the stapedius muscle, observed for the first time in a human fetus of 14 weeks post-conception development (PCd), was brought about by the lack of formation or the regression of the internal segment of the interhyale. It presented a belly of the stapedius muscle with an anomalous arrangement, and with a pseudo tendon originated by the persistence of the external segment of the interhyale., ((c) 2009 Wiley-Liss, Inc.)

The immunocytochemical development of the thoracolumbar sympathetic ganglion and its adrenal counterpart was studied in the chick from days 3.5 to 12 of incubation, using antibodies to 17 separate antigens, including antibodies to pan-neuroendocrine markers, catecholamine-synthesizing and proprotein-processing enzymes, and neuropeptides. Some of the antigens studied (Go protein-alpha subunit, thyrosine hydroxylase, and galanin) were strongly expressed from the first days of development, whereas others (chromogranin-A, chromogranin-B, 7B2 protein, and somatostatin) showed a diverse immunoreactive expression at different stages. Three different patterns were found in the development of both adrenal medulla and thoracolumbar sympathetic ganglion. In the first (chromogranin-A and B, Go protein-alpha subunit, tyrosine hydroxylase, HNK-1, and galanin), virtually all medullary and thoracolumbar sympathetic ganglion cells were strongly immunostained from day 4 onward. Except for HNK-1, chromogranin-A and B, there was a steady increase in immunoreactive cells for all the remaining antigens up to day 12. In the second (7B2 protein, proprotein convertase 2, and secretogranin II), full antigenic expression was reached in medullary and thoracolumbar sympathetic ganglion cells by day 10. In the third pattern (proprotein convertase 3, somatostatin, dopamine-beta-hydroxylase, neuron-specific enolase, vasoactive intestinal polypeptide, and met-enkephalin), differences in immunoreactivity were observed between the medullary and thoracolumbar sympathetic ganglion cells.

During routine bilateral dissection of 64 upper limbs in 32 adult human cadavers, four cases of an axillary arch, a muscular anomaly, were found. In one case, the axillary arch presented on both sides and in two cases it presented unilaterally on the right side. The innervation and relationships of the axillary arches are reported and the surgical significance of the anomaly is discussed., (Copyright 2003 Wiley-Liss, Inc.)

Many studies have been published on the development of the human elbow joint, but authors disagree on its morphogenetic timetable. Most discrepancies center on the cavitation of the elbow joint (including the humeroradial, humeroulnar, and superior radioulnar joints), and the organization of the tunnel of the ulnar nerve. We summarize our observations on the development of the elbow joint in 49 serially sectioned human embryonic (n = 28) and fetal (n = 21) upper limbs. During week 12, ossification begins in the epiphyses of the elements comprising the elbow joint. At the end of the embryonic period, the shallow groove between the posterior aspect of the medial epicondyle and the olecranon process, begins to be visible. The elbow joint cavity appears in O'Rahilly stage 21 (51 days) at the level of the humeroulnar and humeroradial interzones. Formation of the cavity begins at the medialmost portion of the humeroradial interzone and the lateralmost portion of the humeroulnar interzone. The annular ligament begins to develop in O'Rahilly stage 21 (51 days), and the superior radioulnar joint cavity appears between this ligament and the lateral aspect of the head of the radius during O'Rahilly stage 23 (56 days). We established the morphogenetic timetable of the human elbow joint., (Copyright 2000 Wiley-Liss, Inc.)

A human cadaver was studied which presented a biceps brachii with three heads of origin in the left arm. The third or humeral head presented an unique area of insertion into the bicipital aponeurosis (lacertus fibrosus).

A great deal of research has been published on the development of the human temporomandibularjoint (TMJ). However, there is some discordance about its morphological timing. The most controversial aspects concern the moment of the initial organization of the condyle and the squamous part of the temporal bone, the articular disc and capsule and also the cavitation and onset of condylar chondrogenesis. Serial sections of 70 human specimens between weeks 7 and 17 of development were studied by optical microscopy (25 embryos and 45 fetuses). All specimens were obtained from collections of the Institute of Embryology of the Complutense University of Madrid and the Department of Morphological Sciences of the University of Granada. Three phases in the development of the TMJ were identified. The first is the blastematic stage (weeks 7-8 of development), which corresponds with the onset of the organization of the condyle and the articular disc and capsule. During week 8 intramembranous ossification of the temporal squamous bone begins. The second stage is the cavitation stage (weeks 9-11 of development), corresponding to the initial formation of the inferior joint cavity (week 9) and the start condylar chondrogenesis. Week 11 marks the initiation of organization of the superior joint cavity. And the third stage is the maturation stage (after week 12 of development). This work establishes three phases in TMJ development: 1) the blastematic stage (weeks 7-8 of development); 2) the cavitation stage (weeks 9-11 of development); and 3) the maturation stage (after week 12 of development). This study identifies the critical period of TMJ morphogenesis as occurring between weeks 7 and 11 of development.

Purpose: The aim of this work was to clarify the vascular relationships between the middle ear and the temporomandibular joint region during human fetal development., Materials and Methods: Light microscopic studies were done on 40 human fetuses from 72 mm crown-rump length (C-R) to 150 mm C-R, which were stained by various methods. Five human fetuses were dissected. Natural latex with industrial coloring was injected through the external carotid artery. All specimens were dissected bilaterally., Results: The limits of the retroarticular region and the fetal tympanosquamosal fissure are shown. The anterior tympanic artery has a variable origin. In most cases, it originates from the maxillary artery; in other cases it originates from the superficial temporal artery or the bifurcation of the external carotid artery. On its way through the retroarticular region, it gives branches to the posterior part of the temporomandibular joint. It progresses along the most lateral part of the tympanosquamosal fissure, dividing into three branches that extend throughout the middle ear. A number of venous spaces in the retroarticular region that constitute the retrodiscal venous plexus. Small venous vessels along the fetal tympanosquamosal fissure accompany the anterior tympanic artery and drain into the retrodiscal venous plexus., Conclusions: During human fetal development, there is a wide connection across the tympanosquamosal fissure between the middle ear and the temporomandibular joint region. The anterior tympanic artery and its branches, as well as small venous vessels that are connected with the retrodiscal venous plexus, extend along the most lateral part of the fissure.

Background: The aim of this work is to clarify the aspects which are at present most controversial about the development of the anterior segments of Meckel's cartilage, such as the role of and determination of the area that is incorporated in the development of the human mandible., Methods: Light microscope studies were done on 25 embryos and human fetuses from the collection of the Institute of Embryology at the University Complutense of Madrid and the Department of Morphological Science from the University of Granada. Specimen length was between 18 and 125 mm crown-rump., Results: During the embryonic period, Meckel's cartilages were placed in the midline of the mandibular arch but fusion was not observed between them. Ossification of Meckel's cartilage begins at the end of the embryonic period and is completed in the fetal period and the portion that participates in mandibular formation is determined. This segment extends from the mental foramen to near the midline of the mandible. In this region, on the dorsal surface of the symphysis, cartilaginous nodules that originate from Meckel's cartilage are isolated., Conclusions: The ventral portions of Meckel's cartilage do not fuse in the midline of the mandibular arch. These present endo- and perichondral ossification and the section from the mental foramen to near the midline (mandibular symphysis) participates in mandibular formation. The ventral ends of Meckel's cartilage, i.e., the ends nearest the midline, do not ossify and remain isolated on the dorsal surface of the fetal mandibular symphysis.

Background: Many studies have been published on the development of the human knee joint, but scant attention has been given to the development of the knee joint ligaments. The only elements that have received much attention are the cruciate ligaments and their relationships with the synovial membrane., Methods: We summarize our observations on the development of the knee joint ligaments in 50 serially sectioned human embryonic and fetal lower limbs (26 embryos and 24 fetuses)., Results: The patellar ligament begins to form in O'Rahilly stage 20, with the muscle fibers of the quadriceps muscle being attached inferiorly to the tibial tuberosity. The cruciate ligaments (beginning with the posterior) arise from the articular interzone in O'Rahilly stage 21. Subsequently, with the organization of the Wrisberg's meniscofemoral ligament, in week 10 of development, the cruciate ligament system is completed. The lateral collateral ligament begins to form in O'Rahilly stage 23, and from its first appearance it is independent of the knee joint capsule. At this time, development of the tendon of the popliteus muscle begins. The medial collateral ligament begins to develop in week 9 of development as a condensation of the joint capsule. Two weeks later, the intra-articular pad of fat begins to form from mesenchymal tissue below the patella and between the cruciate and the patellar ligaments. With the organization of the suprapatellar bursa in week 14 of development, knee joint development is complete., Conclusions: The morphogenetic time table of the knee joint ligaments was established.

The anterior tympanic artery, a branch of the maxillary artery, ascends through the retroarticular region dividing into anterior branches that spread through the posterior part of the temporomandibular joint, and posterior branches that contribute to the vascularization of the external acoustic meatus and the tympanic cavity. The arrangement of the anterior tympanic artery was studied bilaterally in 18 adult cadavers. In some cases, the anterior tympanic artery branches off from the superficial temporal artery. The relationships of the anterior tympanic artery with the posterior part of the temporomandibular joint were analyzed.