Initial gastrointestinal endocrine cells (GIECs) likely appear at the proximal and distal sites of abdominal intestines and may take a close topographical relation with neural elements in the gut. We examined immunohistochemically-stained sections from 10 fetuses at approximately 8–18 weeks of gestational age (36–155 mm of crown-rump length). Irrespective of whether physiological herniation was present (early 5 specimens) or absent (the other 5), the duodenum and jejunum had well-developed mucosa with villi containing abundant flask-like chromogranin-positive cells. In the earlier 5 specimens, the rectum, standing up to a level of the umbilicus, had a lumen and villi with a few positive cells, but the colon carried neither the lumen or chromogranin-positive cells. The initial GIECs seemed to appear in the basal payer of the epithelium at the distal and proximal foci depending on double pathways of neural crest cell migration. Less number of the colic chromograninpositive cells, more than 5-times difference in density relative to small intestine, was seen in the larger 5 specimens. The appearance of GIECs was delayed at the anal transitional zone (a border area between the columnar and squamous epithelia).The reactivity of neuronal nitric oxide synthase was restricted in the myenteric plexus, whereas clusters of slender calretininpositive cells existed in the lamina propria or core of villi in the duodenum and colon. Relatively small, round or oval positive cells were also seen in the basal layer of the columnar epithelium. Therefore, calretinin-positive cells might exist closely to GIECs in the developing villi.

Meconium is changed from defoliated intestinal villi with apoptosis. A meconium corpuscle is a limited architecture in the meconium at the light microscopic level. In histological and immunohistochemical sections of the abdomen from 40 fetuses at 20–31 weeks of gestation, we found 12 fetuses with meconium and examined the architecture.A solid or loose meconium was seen depending on sites. The solid meconium in the colon and rectum contained numerous spherical or rugby ball-like corpuscles comprising of a core with tightly-packed atrophied cells and a laminar fibrous sheath.The solid meconium surrounded and incorporated villi that maintained the original architecture. The loose meconium was seen not only in the stomach and duodenum but also, depending on specimens, in the colon and rectum. It was composed of a large mucosal fold, a single small villus and/or fragmented epithelia. Notably, these mucosal tissues still contained chromogranin-positive gastrointestinal cells and cytokeratin-positive epithelia. A large ring-like meconium was composed of the entirely circular mucosa or epithelia that seemed to be detached along the muscularis mucosae or the basal lamina.A sheath-like fibrous structure in meconium seemed to originate from the lamina propria and basal lamina of villi. A defoliation of villi with apoptosis seemed difficult to explain a detachment of the entirely circular mucosa or epithelia in large fetuses examined. The latter event might require a specific mechanism such as an in utero intussusception in which a proximal side of the colon was invaginated into the distal lumen.

The nasal mucosa and submucosa likely contain both vascular beds against cold and dry air and resident immunoreactive cells against various antigens. Therefore, a specific fibrous structure seems to be necessary. Using histological specimens from 20 elderly cadavers, we examined the nasal mucosal and submucosal architecture. The ciliated columnar epithelium of the nasal mucosa was characterized by 1) a thick basal lamina, 2) few elastin-positive fibers beneath the epithelium, that was quite different from the nearby mucocutaneous junction area with a thick layer (0.3–0.8 mm) of elastic and oxytalan fibers corresponding to the skin dermis, 3) CD34-positive cells distributing diffusely in the submucosal tissue, and 4) few smooth muscle actin (SMA)-positive fibers beneath the epithelium. Some of submucosal fibrous structure appeared to express both elastin and CD34. CD34-positive arterioles were abundant beneath the ciliated epithelium, but they appeared negative for SMA antibody that cross-reacts with endothelium. Notably, the ciliated columnar epithelium was thin in the lateral wall of the nasal cavity, while the inferior concha carried the thick pseudostratified columnar epithelium.Strangely, the inferior or palatal wall of the nasal cavity was covered by the thick stratified epithelium. We found SMApositive mucosal venous plexus in the lateral wall of nasal cavity, but the submucosa was filled with glands in the inferior concha. Vascular beds might be replaced by glands in the nasal submucosa. The site-dependent difference in the mucosal morphology as well as the absence of vascular beds might be a result of secondary change with aging.

Neck epaxial muscles, which are differentiated for suspending the head, occupy a large space posterior to the cervical lordosis. Limited information exists regarding developmental process that determines the muscle fiber direction and bony attachment of neck epaxial muscles. We examined histological sections of 28 human fetuses aged approximately 7–18 weeks (crown-rump length, 20–150 mm). In place of the underdeveloped lordosis, the transverse process of cervical vertebrae was shifted anteriorly at the cervicothoracic junction. The semispinalis and longissimus were distinguished by the direction of muscle fibers connecting between the surface aponeurosis and transverse process. The semispinalis capitis and splenius capitis had a bulky anterior margin without bony attachments. The obliquus capitis inferior continued to both the rectus capitis posterior major and the semispinalis cervicis, but the obliquus capitis superior was consistently independent. Muscle attachments to the scapula were quite different from the final morphology: 1) the levator and rhomboidei usually extended inferiorly along the developing scapula beyond the inferior angle and 2) the splenius capitis or semispinalis cervicis rarely issued an aberrant bundle attaching to the scapula. The scaleni, rhomboidei, levator scapulae, iliocostalis and longissimus were arranged in parallel from the anteromedial to the posterolateral planes and together formed a thick oblique muscle bundle originating from the cervical transverse process and running toward the upper thoracic vertebra and ribcage. The transient oblique muscle bundle seen in early fetuses seemed to provide the so-called intermediate axial muscle between the epaxial-hypaxial muscles: a concept postulated in recent molecular neurology and embryology.

Although human lymph node architecture varies by site, the intranodal distribution of interdigitating dendritic cells (DCs) remains poorly understood. To address this, we compared the morphology of submandibular, paratracheal, mesenteric, and inguinal nodes obtained from 24 donated cadavers. Immunoreactivity was evaluated by comparing these cadaveric nodes with surgically resected lymph nodes obtained from five old-aged patients with nonmetastatic cancer.Despite the limited number of dendritic cell-specific ICAM-3–grabbing nonintegrin (DC-SIGN)–positive cells (candidate DCs) in cadaveric specimens, these tissues were deemed suitable for analysis. The submandibular and paratracheal nodes exhibited a belt-like cortex, with paracortical lymph sinus extending from the subcapsular sinus and surrounding the follicle.In contrast, the mesenteric and inguinal nodes contained multiple island-like cortices separated by thick paracortical lymph sinuses. Endothelial cells lining all lymph sinuses showed reactivity for smooth muscle actin and DC-SIGN. Macrophages and candidate DCs were abundant in the paratracheal and mesenteric node sinuses but scarce in the submandibular and inguinal nodes. Notably, the medullary sinus in the submandibular and inguinal nodes was filled with fibrous tissue, and the surrounding paracortical sinuses formed a “sea” around the island-like cortices, often resulting in loss of nodal polarization.Although the proportional area occupied by candidate DCs per nodal section was almost the same at the four sites, the overlap between DCs and macrophage clusters was small in paratracheal and inguinal nodes. The amount of afferent lymph and the retention of efferent lymph might determine the site-dependent architecture. Therefore, in aged nodes, DCs were preferentially localized in the paracortical sinus.

The occipital bone squamosa (OCS) is unique because of its double origin from both endochondral and membranous bones. The present study attempted to demonstrate the process of connection between these two bone types. We examined sagittal and frontal histological sections from 29 human fetuses with a crown-rump length ranging from 38 to 328 mm (approximately 7–39 weeks of gestational age [GA]). An initial cartilage plate appeared in the posterior side of the fourth ventricle at GA 7–8 weeks and extended inferiorly to connect with the cartilaginous basioccipital and condyle. At GA 9–10 weeks, on the superior side of the cartilage plate, membranous bone fragments appeared and adopted an arrangement resembling a chain of irregularly-shaped beads.They did not form a complete plate-like bone until late-term. At GA 11–12 weeks, endochondral ossification centers appeared at the upper and lower ends of the cartilage plate. At GA 12–15 weeks, a bar-like periosteal bone developed near and superior to the upper ossification center. Notably, sinusoidal structures, which were surrounded by growing periosteal bones, contained islandlike clusters of calcified cartilage fragments. Therefore, the upper ossification center appeared likely to “migrate” downward and become distant from membranous bones. The extending periosteal bone reached and joined the membranous bone fragments.Consequently, the periosteal bones connected between the endochondral and membranous bones in the OCS. This connection was quite different from the other components of the calvaria, where membranous bones overlap the skull base cartilages at the margin.

The temporal fascia is a double lamina sandwiching a thick fat layer above the zygomatic bony arch. To characterize each lamina, their developmental processes were examined in fetuses. We observed histological sections from 22 half-heads of 10 mid-term fetuses at 14–18 weeks (crown-rump length, 95–150 mm) and 12 near-term fetuses at 26–40 weeks (crown-rump length, 215–334 mm). The superficial lamina of the temporal fascia was not evident at mid-term. Instead, a loose subcutaneous tissue was attached to the thin, deep lamina of the temporal fascia covering the temporalis muscle. At near-term, the deep lamina became thick, while the superficial lamina appeared and exhibited several variations: i) a monolayered thick membrane (5 specimens); ii) a multi-layered membranous structure (6) and; iii) a cluster of independent thick fasciae each of which were separated by fatty tissues (1). In the second and third patterns, fatty tissue between the two laminae was likely to contain longitudinal fibrous bands in parallel with the deep lamina. Varying proportions of the multi-layered superficial lamina were not attached to the zygomatic arch, but extended below the bony arch. Whether or not lobulation or septation of fatty tissues was evident was not dependent on age. The deep lamina seemed to develop from the temporalis muscle depending on the muscle contraction. In contrast, the superficial lamina developed from subcutaneous collagenous bundles continuous to the cheek. Therein, a difference in development was clearly seen between two categories of the fasciae.

Striated muscle insertions into the skin and mucosa are present in the head, neck, and pelvic floor. We reexamined the histology of these tissues to elucidate their role in transmission of the force. We examined histological sections of 25 human fetuses (gestational ages of ~11–19 weeks and ~26–40 weeks) and 6 cadavers of elderly individuals. Facial muscle insertion or terminal almost always formed as an interdigitation with another muscle or as a circular arrangement in which muscle fiber insertions were sandwiched and mechanically supported by other muscle fibers (like an in-series muscle). Our examination of the face revealed some limited exceptions in which muscle fibers that approached the dermis were always in the nasalis and mentalis muscles, and often in the levator labii superioris alaeque nasi muscle. The buccinator muscle was consistently inserted into the basement membrane of the oral mucosa. Parts of the uvulae muscle in the soft palate and of the intrinsic vertical muscle of the tongue were likely to direct toward the mucosa. In contrast, the pelvic floor did not contain striated muscle fibers that were directed toward the skin or mucosa. Although ‘cutaneous muscle’ is a common term, the actual insertion of a muscle into the skin or mucosa seemed to be very rare. Instead, superficial muscle insertion often consisted of interdigitated muscle bundles that had different functional vectors. In this case, the terminal of one muscle bundle was sandwiched and fixed mechanically by other bundles.

Striated muscle fiber crossings at almost right angle are known to exist in the face, soft palate, pharyngeal wall and tongue. We aimed to identify a specific interface tissue at the crossing. We observed histological sections from 22 halfheads of 12 near-term fetuses at 26–40 weeks (crown-rump length, 215–334 mm). For comparison, we also observed tongue frontal sections from 5 elderly cadavers (75–85 years old). At the angle of mouth as well as in the soft palate and pharyngeal wall, a solitary striated muscle fiber (e.g., levator) consistently crossed a fiber bundle of the antagonist muscle (e.g., depressor), but a solitary-to-solitary fiber interdigitation was unlikely with the antagonist muscle. Near the external nasal orifice as well as in the tongue intrinsic muscle layer, at every section, there was a crossing with an endomysium-to-endomysium contact:the nasalis and platysma muscles and; the vertical and transverse (or inferior longitudinal) tongue muscles. Therein, the functional vectors crossed at almost right angle. Also in adult tongue, the vertical and transverse muscle fibers sometimes (0–2 sites per section) crossed with an endomysium-to-endomysium contact. At the muscle crossing with an endomysium contact, the endomysium and basement membrane seemed to receive a friction stress between two muscles. Although some crossings might disappear due to high muscle activity after birth, not a few of them were likely to maintain. To minimize the mechanical stress, a minute nervous control of the timing, duration and strength of muscle contraction seemed to be necessary.

Striated muscle fiber crossings at almost right angle are known to exist in the face, soft palate, pharyngeal wall and tongue. We aimed to identify a specific interface tissue at the crossing. We observed histological sections from 22 halfheads of 12 near-term fetuses at 26–40 weeks (crown-rump length, 215–334 mm). For comparison, we also observed tongue frontal sections from 5 elderly cadavers (75–85 years old). At the angle of mouth as well as in the soft palate and pharyngeal wall, a solitary striated muscle fiber (e.g., levator) consistently crossed a fiber bundle of the antagonist muscle (e.g., depressor), but a solitary-to-solitary fiber interdigitation was unlikely with the antagonist muscle. Near the external nasal orifice as well as in the tongue intrinsic muscle layer, at every section, there was a crossing with an endomysium-to-endomysium contact:the nasalis and platysma muscles and; the vertical and transverse (or inferior longitudinal) tongue muscles. Therein, the functional vectors crossed at almost right angle. Also in adult tongue, the vertical and transverse muscle fibers sometimes (0–2 sites per section) crossed with an endomysium-to-endomysium contact. At the muscle crossing with an endomysium contact, the endomysium and basement membrane seemed to receive a friction stress between two muscles. Although some crossings might disappear due to high muscle activity after birth, not a few of them were likely to maintain. To minimize the mechanical stress, a minute nervous control of the timing, duration and strength of muscle contraction seemed to be necessary.