Fetal Tendinous Connection Between the Tensor Tympani and Tensor Veli Palatini Muscles: A Single Digastric Muscle Acting for Morphogenesis of the Cranial Base

Some researchers contend that in adults the tensor tympani muscle (TT) connects with the tensor veli palatini muscle (TVP) by an intermediate tendon, in disagreement with the other researchers. To resolve this controversy, we examined serial sections of 50 human embryos and fetuses at 6–17 weeks of development. At 6 weeks, in the first pharyngeal arch, a mesenchymal connection was found first to divide a single anlage into the TT and TVP. At and after 7 weeks, the TT was connected continuously with the TVP by a definite tendinous tissue mediolaterally crossing the pharyngotympanic tube. At 11 weeks another fascia was visible covering the cranial and lateral sides of the tube. This “gonial fascia” had two thickened borders: the superior one corresponded to a part of the connecting tendon between the TT and TVP; the inferior one was a fibrous band ending at the os goniale near the lateral end of the TVP. In association with the gonial fascia, the fetal TT and TVP seemed to provide a functional complex. The TT–TVP complex might first help elevate the palatal shelves in association with the developing tongue. Next, the tubal passage, maintained by contraction of the muscle complex, seems to facilitate the removal of loose mesenchymal tissues from the tympanic cavity. Third, the muscle complex most likely determined the final morphology of the pterygoid process. Consequently, despite the controversial morphologies in adults, the TT and TVP seemed to make a single digastric muscle acting for the morphogenesis of the cranial base. Anat Rec, 299:474–483, 2016. © 2016 Wiley Periodicals, Inc.     

Histological study of the developing pterygoid process of the fetal mouse sphenoid

The pterygoid process undergoes ossification of both the cartilage and membrane. However, few studies have attempted to explore the sequential development of the pterygoid process. Using histological examination, we performed morphological observations of the pterygoid process and surrounding tissue. ICR mice at embryonic days 13.5–18.0 and postnatal day 0 were used for morphological observations of the pterygoid process. By embryonic day 14.5, a mesenchymal cell condensation forming the anlage of the future medial pterygoid process differentiated into osteoid-like tissue and cartilage. At embryonic days 15.5–16.5, cartilage cells were clearly evident in the medial pterygoid process. In the medial pterygoid process, a bone collar was evident and calcified bone tissue surrounded the cartilage. At this point, a mesenchymal cell condensation formed the anlage of the pterygoid hamulus. At embryonic days 17.0–18.0, the cartilages were located along the lower and posterior border of the medial pterygoid process. A metachromatically stained matrix first became detectable around cells located in the pterygoid hamulus. On the other hand, at embryonic day 13.5, a metachromatically stained matrix was already evident in the space between the flattened cells in the lateral pterygoid process. At embryonic day 17.0, a hypertrophic cell zone had clearly formed in the diaphysis. On the basis of our present investigation, the lateral pterygoid process can be classified as primary cartilage, whereas the medial pterygoid process can be classified as secondary cartilage. Furthermore, it was found that the pterygoid hamulus is formed latest in the medial pterygoid process.     

Early fetal development of hard tissue pulleys for the human superior oblique and tensor veli palatini muscles

The trochlea for the superior oblique muscle as well as the hamulus for the tensor veli palatini muscle is well known as a fibrocartilage-associated, hard tissue pulley that changes the direction of the tendon. However, details of the fetal development of these structures remain obscure. We carried out a histological study of hematoxylin-eosin-stained preparations from 20 human fetuses (7-15 weeks of gestation) and clarified a common rule for the formation of these pulleys: changing in the location of a structure for the muscle insertion. At the early stage, the muscle and insertion exhibit an almost straight course alongside the primitive pulley, but because the structure for insertion later moves away from a straight line along which the muscle acts, the tendon begins to turn around the cartilage by 12 weeks. The posterior shift of the soft palate is clearly evident, but rotation of the sclera or eyeball is difficult to identify in sections. To some degree, the trochlea may originate from a common anlage with the sclera. We hypothesize that, from the evolutionary point of view, the hamulus or trochlea do not form for the pulley itself but as a structure independent of the related muscle function. The fetal topographical anatomy around the tensor veli palatini, as well as its relationship to the tensor tympani, is also described.     

A re-evaluation of the premaxillary bone in humans

The discovery of the premaxillary bone (os incisivum, os intermaxillare or premaxilla) in humans has been attributed to Goethe, and it has also been named os Goethei. However, Broussonet (1779) and Vicq dAzyr (1780) came to the same result with different methods. The first anatomists described this medial part of the upper jaw as a separate bone in the vertebrate skull, and, as we know, Coiter (1573) was the first to present an illustration of the sutura incisiva in the human. This fact, and furthermore its development from three parts:—(1) the alveolar part with the facial process, (2) the palatine process, and (3) the processus Stenonianus—can no longer be found in modern textbooks of developmental biology. At the end of the nineteenth and in the early twentieth century a vehement discussion focused on the number and position of its ossification centers and its sutures. Therefore, it is hard to believe that the elaborate work of the old embryologists is ignored and that the existence of a premaxillary bone in humans is even denied by many authors. Therefore this re-evaluation was done to demonstrate the early development of the premaxillary bone using the reconstructions of Felber (1919), Jarmer (1922) and data from our own observations on SEM micrographs and serial sections from 16 mm embryo to 68 mm fetus. Ossification of a separate premaxilla was first observed in a 16 mm embryo. We agree with Jarmer (1922), Peter (1924), and Shepherd and McCarthy (1955) that it develops from three anlagen, which are, however, not fully separated. The predominant sutura incisiva (rudimentarily seen on the facial side in a prematurely born child) and a shorter sutura intraincisiva argue in this sense. The later growth of this bone and its processes establish an important structure in the middle of the facial skull. Its architecture fits well with the functional test of others. We also focused on the relation of the developing premaxilla to the forming nasal septum moving from ventral to dorsal and the intercalation of the vomer. Thus the premaxilla acts as a stabilizing element within the facial skeleton comparable with the keystone of a Roman arch. Furthermore, the significance of the premaxillary anlage for the closure of the palatine was documented by a synopsis made from a stage 16, 10.2 mm GL embryo to a 49 mm GL fetus. Finally the growth of the premaxilla is closely related to the development of the human face. Abnormal growth may be correlated to characteristic malformations such as protrusion, closed bite and prognathism. Concerning the relation of the premaxillary bone to cleft lip and palate we agree with others that the position of the clefts is not always identical with the incisive suture. This is proved by the double anlagen of an upper–outer incisor in a 55 mm fetus and an adult.     

翼腭间隙的矢、冠状断层解剖及临床意义

目的为翼腭间隙疾病的影像诊断提供解剖学资料。方法选用成尸头颈部40例制成连续矢、冠状断面,观察翼腭间隙及其结构的解剖学关系,利用游标卡尺及求积仪分别测量其径线和面积。结果翼腭间隙呈漏斗状或四边形,经翼窝和眶下裂层面的面积分别为(78.6±4.22)mm2(左)、(79.1±4.60)mm2(右),(244.0±5.18)mm2(左)、(248.6±5.64)mm2(右),两侧翼腭间隙及其结构呈对称性,径线和面积均无显著性差异(P>0.05)。矢状断面能较好显示翼腭管、腭大管及腭小管的连续性,冠状断面利于观察翼腭间隙顶壁、圆孔、眶下裂、翼管及其与蝶窦的关系。结论翼腭间隙的矢、冠状断层解剖对疾病的影像诊断具有重要意义。     

A light and electron microscopic study on the embryonic development of the rat carotid body

The embryonic development of the rat carotid body was studied with electron microscopy. In the 11 mm embryo a cell aggregation consisting of undifferentiated cells and unmyelinated nerve fibers appears on the anterior wall of the third branchial artery. Granule-containing cells appear in the 12 mm embryo and continue to increase in number as the cellular aggregation increases in size and becomes separated from the wall of the third branchial artery. Synapse formation and the appearance of fenestrated capillaries occur almost simultaneously at the 17 mm stage. There are two types of synapses, one with membrane densification and vesicles clustered inside the nerve endings, the other with dense material and vesicles inside the granule-containing cells. At the 20 mm stage the undifferentiated cells send enveloping cytoplasmic processes toward adjacent granule-containing cells and the carotid body anlage displays rudimentary lobules.     

Relations of the pterygoid hamulus and hard palate in children and adults: anatomical implications for the function of the soft palate.

We investigated spatial relations of the pterygoid hamuli to the hard palate on 65 skull bases: 31 disarticulated sphenoidal bones from the newborn up to 9 years of age, 19 skulls of adult skeletons (21-59 age group), and 15 skulls aged 60-100 years. We measured: (a) width of the hard palate in the choanal region, (b) length of the hamulus, (c) inclination of the hamulus from the perpendicular line, and (d) distance between the tips of the contralateral hamuli. The width of the hard palate in the choanal region was smallest in children (mean +/- standard deviation, 21.5 +/- 2.6 mm) compared with adult skulls (26.8 +/- 2.3 mm in the 21-59 age group and 25.4 +/- 1.9 mm in the 60-100 age group; P<0.05, one-way analysis of variance (ANOVA) and Student-Newman-Keuls post hoc test). Children had the shortest hamulus (3.6 +/- 1.5mm), and its length increased in the adult age group to 6.9+1.7mm (P<0.05), and then again decreased to 5.0 +/- 1.9 mm in the 60-100 age group (P<0.05 vs. adults and children). The distance between the tips of the contralateral hamuli and their lateral inclination from the perpendicular plane were also greater in the adult age group (38.0 +/- 2.7mm and 35.9 +/- 13.7 degrees, respectively) than either in children (31.0 +/- 3.7mm and 19.6 +/- 12.1 degrees) or the elderly (32.7 +/- 3.9mm and 19.7 +/- 10.3 degrees) (P<0.05). Our study showed that the anatomical measures of the pterygoid hamulus and its relation to the surrounding structures change with age, and occur with the changes in the function of pharyngeal and palatal muscles in deglutition. These changes may have clinical relevance for sleep apnoea and snoring.     

Aberrant muscle between the temporalis and the lateral pterygoid muscles: M. pterygoideus proprius (Henle).

During examination of the positional relationships between the lateral pterygoid and the temporalis muscles and the innervating nerves, an aberrant muscle was observed in three of 66 head halves. The aberrant muscle originated from the medial surface of the anteromedial muscle bundle of the temporalis (Shimokawa et al. 1998, Surg. Radiol. Anat. 20:329-334) and inserted into the inferolateral surface of the lower head of the lateral pterygoid. Due to its location, origin and insertion this aberrant muscle slip is considered to correspond to the pterygoideus proprius described by Henle (1858, Handbuch der Anatomie des Menschen). Based on the innervation findings, the present aberrant muscle might be considered as a remnant muscle bundle between the anteromedial muscle bundle of the temporalis and the lateral pterygoid during differentiation of the lateral masticatory muscle anlage.     

Representation of the tensor veli palatini muscle in the trigeminal motor nucleus of the Japanese monkey (Macaca fuscata)

Distribution of motoneurons supplying the tensor veli palatini (TVP) muscle was examined in the Japanese monkey (Macaca fuscata) by the retrograde horseradish peroxidase (HRP) method. Neurons labeled with HRP which was injected into the tensor veli palatini muscle were seen in the ventromedial aspects of the dorsolateral division of the trigeminal motor nucleus, at all rostrocaudal levels of the trigeminal motor nucleus. The vast majority of these TVP motoneurons were distributed around the margin, especially the dorsal margin, of the cluster of motoneurons which innervate the lateral pterygoid muscle.     

Functional morphology of the pterygoid hamulus.

The pterygoid hamulus (PH), a structure on the under surface of the skull base which has so far hardly been described, is in a peculiar situation biomechanically. The aim of this study is to accumulate sufficient morphological data to enable a functional interpretation to be provided. A total of 93 adult skulls and 24 children's skulls have been examined, and also an additional 20 heads in which the relationship to the surrounding muscles could be investigated. Measurements were made with a sliding gauge, and sections cut from specimens embedded in methyl methacrylate were examined histologically. The hamulus is a variable structure which can, however, be allotted to one of a few basic types. As nomenclature we suggest the following terms: the base: Basis; body: Corpus, sulcus: Sulcus; neck: Collum; head: Caput of the hamulus. The average measurements are: length 7.2 mm, sagittal breadth 1.4 mm, transverse breadth 2.3 mm. The sections show that the medial cortical lamella is thicker than the lateral, and that the 2 are bound together by oblique trabeculae. The medial gradient angle of the collagen fibers is smaller than that of the lateral. A few muscles take origin from the hamulus, the tensor veli palatini turns round the neck, and a few of its fibers take origin here. The distribution of the material within the hamulus suggests that its body is subjected to greater loading in the medio-dorsal direction, but that the head is freely pulled away laterally and caudally. Its exposed position at the distal end of the upper dental arch and the formation of a bursa or sliding layer in the sulcus suggest that it may be a potential source of irritation.     

Three‐dimensional imaging of palatal muscles in the human embryo and fetus: Development of levator veli palatini and clinical importance of the lesser palatine nerve

Background: After palatoplasty, incomplete velopharyngeal closure in speech articulation sometimes persists, despite restoration of deglutition function. The levator veli palatini (LVP) is believed to be significantly involved with velopharyngeal function in articulation; however, the development and innervation of LVP remain obscure. The development of LVP in human embryos and fetuses has not been systematically analyzed using the Carnegie stage (CS) to standardize documentation of development. Results: The anlage of LVP starts to develop at CS 21 beneath the aperture of the auditory tube (AT) to the pharynx. At CS 23, LVP runs along AT over its full length, as evidenced by three‐dimensional image reconstruction. In the fetal stage, the lesser palatine nerve (LPN) is in contact with LVP. Conclusions: The positional relationship between LVP and AT three‐dimensionally, suggesting that LVP might be derived from the second branchial arch. Based on histological evidence, we hypothesize that motor components from the facial nerve may run along LPN, believed to be purely sensory. The multiple innervation of LVP by LPN and pharyngeal plexus may explain the postpalatoplasty discrepancy between the partial impairment in articulation vs. the functional restoration of deglutition. That is, the contribution of LPN is greater in articulation than in deglutition. Developmental Dynamics 245:123–131, 2016. © 2015 Wiley Periodicals, Inc.     

Structure of the middle ear and auditory tube in the house musk shrew, Suncus murinus

Anatomical features of the middle ear and auditory tube (AT) in the house musk shrew, Suncus murinus, were examined by dissection and light microscopy. The tensor veli palatini (TVP) and tensor tympani (TT) have no connections with the wall or cartilage of the AT although they are connected by the intermediate tendon. None of the levator veli palatini (LVP) muscle bundles are attached to the AT. The salpingopharyngeus (SA) alone has its origin on the caudal edge of the tubal cartilage. The origin extends to the pharyngeal two thirds of the cartilage. The SA originates perpendicular to the AT and runs caudomedialward. Some SA muscle bundles intermingle with those of the palatopharyngeus to end on the dorsal wall of the pharynx. The observations provide no evidence that the TVP, LVP and TT have any role in AT function. The only muscle affecting the AT function in S. murinus is the SA, and it would be the AT dilator.     

Reconstructing the pathway of the tensor veli palatini motor nerve during early mouse development

The motor axons innervating the tensor veli palatini (TVP) navigate a long distance from the trigeminal motor nucleus to their target. The pathway and time course of the TVP motor nerve during this navigation process remain poorly understood. The aim of this study was to elucidate the peripheral development of the TVP motor nerve, and to confirm when the morphological relationship is established between the nerve and target muscle progenitors. Using immunohistochemistry, carbocyanine fluorescent labeling, and computerized three-dimensional image-reconstruction methods, we demonstrated the development of the TVP motor nerve in mouse embryos. Further, the morphological relationship between the extending mandibular nerve and myogenic cells stained for MyoD1 was examined. The peripheral pathfinding of the TVP motor nerve was divided into three continuous stages: (1) the earliest trigeminal motor axons leave the metencephalon and enter the primordium of the trigeminal ganglion at E9.5, when MyoD1-positive cells can already be detected in the mesenchymal core of the mandibular arch; (2) converging with the sensory root, the trigeminal motor root excites the trigeminal ganglion and begins to approach the mandibular muscle precursors at E10.5; (3) collateral branching occurs at E12.5. By E13.5, a nerve branch splits from the mandibular nerve to innervate the TVP, which appears as an individual muscle mass. These results suggest that the early process of mandibular motor nerve extension is correlated with the trigeminal ganglion cells, whereas when growing out of the ganglion, the mandibular nerve has a close relationship with target myogenic cells throughout the later process of pathway finding.     

人胎副睾与输精管的组织学观察

取16－28周24例布依族人胎副睾及输精管，HE，PAS染色，示16周副睾上皮呈假复层柱状，胞质含较多粗大PAS阳性颗粒，游离面有纤毛，上皮基膜呈PAS阳性反应，随着胎龄增加，管腔增大，上皮变高，28周副睾管腔平整，上皮外有环行平滑肌，睾丸输出管呈明显不规则形，16周时输精管上皮呈单层柱状，肌层不明显，19周上皮已呈假复层柱状，未见纤毛，随着胎龄增加纤毛出现，环行肌层次增加后纵行肌出现，上皮基膜，纤毛呈PAS阳性反应，为研究人胎生长发育，提供形态学基础。     

颞下窝的CT影像与断层标本对照研究及临床意义

目的:为颞下窝病变的影像诊断及手术入路提供解剖学资料.方法:选取志愿者40名,在螺旋CT机上以眦耳线(CML)为基线对颞下窝结构进行层厚1mm连续扫描.选取成人尸体头颈部标本20例,以CML为基线制成层厚5mm连续断层标本.在经冠突和茎突末端层面的CT影像及断层标本上,观察颞下窝及其邻近结构的解剖学关系,测量其长径、宽径和面积.结果:颞下窝的形态呈不规则状,在CT影像和断层标本上经冠突、茎突末端层面的面积分别为(1055.6 +2.05)mm2和(1034.5±3.32) mm2、(356.6±1.78) rm2和(345.8±1.89) mm2.两侧颞下窝及其结构呈对称性,长径、横径和面积侧别间比较差异均无统计学意义(P＞0.05).自茎突至翼突外侧板前缘或翼突内侧板后缘的连线可区分颞下窝与咽旁间隙,茎突、冠突、翼外肌、翼突外侧板和翼突内侧板是CT影像诊断的重要解剖学标志.结论:颞下窝的CT影像与断层标本的解剖对照研究,对颞下窝肿瘤等疾病的影像诊断及指导手术入路具有重要临床意义.     

Clinical anatomy of the posterior maxilla pertaining to Le Fort I osteotomy in Thais

This article studies the anatomy of the posterior maxilla pertaining to bone-cut design of Le Fort I osteotomy to avoid the injury to the descending palatine artery in Thais. Fifty-five skulls (38 males, 17 females) were assessed for the anatomical landmarks by a combination of direct inspection, computerized imaging, and computed tomography scan analysis. The results showed that 27.28% of the pterygomaxillary junction (PMJ) became synostosis. The mean heights of the PMJ, posterior maxilla, and maxillary tuberosity were 15.14 +/- 2.46 mm, 22.51 +/- 3.50 mm, and 7.45 +/- 2.76 mm, respectively. The mean length of the medial sinus wall measuring from the piriform rim to the descending palatine canal at the Le Fort I level was 34.40 +/- 2.96 mm. The mean widths of the posterior incision of Le Fort I osteotomy at the maxillary tuberosity and PMJ were 20.38 +/- 2.82 mm and 11.60 +/- 1.57 mm. The mean length of the posterior maxilla was 27.18 +/- 2.49 mm. Distances from the greater palatine foramen to the maxillary tuberosity incision and PMJ incision were 1.76 +/- 1.12 mm and 3.59 +/- 1.40 mm. The mean angle between the descending palatine canal and the hard palate was 57.33 +/- 4.54 degrees . There were no significant differences in any measurements between sides and genders, except the pterygoid process width and posterior maxilla length of males were longer than those of females (P < 0.05). This study could provide better understanding of the posterior maxillary anatomy that is important for the bone-cut design of Le Fort I osteotomy to avoid excessive intraoperative and postoperative hemorrhage including ischemia of the mobilized maxilla.     

翼腭间隙通道的CT三维重建及临床意义

目的　为翼腭间隙通道及其邻近结构病变的影像诊断和内镜手术提供解剖学资料。 方法　选取志愿者40名,在螺旋CT机上沿眦耳线（CML）连续扫描,将原始图像数据输入CT三维重建工作站,采用多平面重组技术（MPR）,沿翼腭间隙各通道长轴和垂直于各通道长轴分别进行CT图像重建。观察翼腭间隙通道的位置、形态及毗邻结构,测量其径线。 结果　MPR重建CT影像可清楚显示翼腭间隙通道的圆孔、翼管、蝶腭孔、眶下裂、翼上颌裂、翼腭管、腭大管、腭小管、腭鞘管和犁鞘管的位置、形态及其毗邻结构,左、右侧翼腭间隙通道呈对称性分布,各径线均无显著性差异（P>0.05）。圆孔、翼管、腭鞘管和犁鞘管位于蝶窦周围,可轻度或明显凸入蝶窦腔内。圆孔和翼管分别位于蝶窦腔的上、下方,长度（4.05±　0.81）mm和（14.49±1.60）mm,冠状重建影像可较清晰显示其位置关系。 结论　翼腭间隙通道的CT三维重建对翼腭间隙通道及其邻近结构病变的影像诊断和内镜手术具有重要的临床意义。     

Fetal developmental change in topographical relationship between the human lateral pterygoid muscle and buccal nerve

In adults, the lateral pterygoid muscle (LPM) is usually divided into the upper and lower heads, between which the buccal nerve passes. Using sagittal or horizontal sections of 14 fetuses and seven embryos (five specimens at approximately 20-25 weeks; five at 14-16 weeks; four at 8 weeks; seven at 6-7 weeks), we examined the topographical relationship between the LPM and the buccal nerve. In large fetuses later than 15 weeks, the upper head of the LPM was clearly discriminated from the lower head. However, the upper head was much smaller than the lower head in the smaller fetuses. Thus, in the latter, the upper head was better described as an 'anterior slip' extending from the lower head or the major muscle mass to the anterior side of the buccal nerve. The postero-anterior nerve course seemed to be determined by a branch to the temporalis muscle (i.e. the anterior deep temporal nerve). At 8 weeks, the buccal nerve passed through the roof of the small, fan-like LPM. At 6-7 weeks, the LPM anlage was embedded between the temporobuccal nerve trunk and the inferior alveolar nerve. Therefore, parts of the LPM were likely to 'leak' out of slits between the origins of the mandibular nerve branches at 7-8 weeks, and seemed to grow in size during weeks 14-20 and extend anterosuperiorly along the infratemporal surface of the prominently developing greater wing of the sphenoid bone. Consequently, the topographical relationship between the LPM and the buccal nerve appeared to 'change' during fetal development due to delayed development of the upper head.