Positional changes in tendon insertions from bone to fascia: development of the pes anserinus and semimembranosus muscle insertion in human foetuses

Growing stylohyoideus muscle insertion to the hyoid bone with special reference to its topographical relation to the intermediate tendon of digastricus muscle: A histological study using human fetuses

BACKGROUND

In adults, the intermediate tendon of digastricus muscle usually runs along the medial or lateral side of the stylohyoideus muscle insertion. To provide a better understanding of the variations, we examined the topographical anatomy of the muscle and tendon in fetuses.

METHODS

We examined histological sections from six early-term, 26 mid-term and six near-term fetuses (approximately 8-9, 12-18 weeks and 25-33 weeks).

RESULTS

At early-term, an initial sheath of intermediate tendon of digastricus muscle received the stylohyoideus muscle at the superior aspect. The muscle and tendon was distant from the hyoid. At mid-term, near the insertion to the hyoid greater horn, the stylohyoideus muscle consistently surrounded more than 2/3 of the intermediate tendon circumference. In contrast, we found no near-term specimen in which the stylohyoideus muscle surrounded the intermediate tendon. The multilayered tendon sheath was fully developed until near-term and connected to the body of hyoid by an intermuscular septum between the thyrohyoideus muscle and one or two of suprahyoid muscles. Therefore, the hyoid insertion of the styloglossus muscle was a transient morphology at mid-term.

CONCLUSION

The stylohyoideus muscle insertion was appeared to move from the tendon sheath to the hyoid greater horn and, until near-term, return to the tendon sheath. A fascia connecting the tendon sheath to the body of hyoid was strengthened by the suprahyoid and infrahyoid muscles. The latter muscles seemed to regulate fixation/relaxation of the intermediate tendon to the hyoid. The stylohyoideus muscle slips sandwiching the intermediate tendon might be a rare morphology.

Human orbital muscle in adult cadavers and near-term fetuses: its bony attachments and individual variation identified by immunohistochemistry

PURPOSE

To compare fetal and adult morphologies of the orbital muscle (OM) and to describe the detailed topographical anatomy in adults.

METHODS

Using unilateral orbits from 15 near-term fetuses and 21 elderly cadavers, semiserial horizontal or sagittal paraffin sections were prepared at intervals of 20-100 µm. In addition to routine histology, we performed immunohistochemistry for smooth muscle actin.

RESULTS

At near term, the OM consistently extended widely from the zygomatic bone or the greater wing of the sphenoid to the maxilla or ethmoid. Thus, it was a large sheet covering the future inferior orbital fissure. In contrast, the adult OM was a thin and small muscle bundle connecting (1) the greater wing of the sphenoid to the maxilla (11/19 cadavers), (2) the lesser wing of the sphenoid to the maxilla (5/19) or the greater wing (3/19). The small OM was likely to be restricted within the greater wing (5/19 cadavers) or the maxilla (3/19). Two of these five types of OM coexisted in eight orbits. OM attachment to the lesser wing was not seen in fetuses, whereas ethmoid attachment was absent in adults.

CONCLUSIONS

The lesser wing attachment of the OM seemed to establish after birth. A growing common origin of the three recti was likely involved in "stealing" the near-term OM attachment from the ethmoid. The strong immunoreactivity of remnant-like OM in the elderly suggests that OM contraction is still likely to occur against the increased flow through a thin vein. However, the contraction might have no clinical significance.

Transient connection or origin of the inferior pharyngeal constrictor during fetal development: A study using human fetal sagittal sections

The inferior pharyngeal constrictor (IPC) originates from the thyroid and cricoid cartilages and inserts to the pharyngeal raphe. In serial sagittal sections of 37 embryos and fetuses at 6-15 weeks (crown rump length 15-115mm), we found (1) the IPC connecting to the sternothyroideus and thyrohyoideus muscles (16 fetuses at 6-11 weeks) or (2) the cricothyroideus muscle (6 fetuses at 12-15 weeks) in addition to the usual cricoid origin. These aberrant connections were most likely to be transient origins of the IPC not from a hard tissue but nearby striated muscles. In four of the latter six specimens, a tendinous band from the IPC inferior end connected to the cricothyroideus muscle to provide a digastric muscle-like appearance. These aberrant connections with nearby muscles seemed to become separated by a growing protrusion of the thyroid cartilage. Therefore, these aberrant origins were, even if developed, most likely to be "corrected" to the adult morphology during midterm or late prenatal period. The aberrant or transient origin of the IPC seemed to result from a discrepancy in growth of the cartilage and muscles. Such a discrepancy in growth seems to resemble the IPC wrapping around the superior cornu of thyroid cartilage. In addition, a final or adult-like morphology was found in two of the present 37 fetal specimens. It seemed to suggest a significant redundancy in growth rate of the laryngeal structures.

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.

The palatomaxillary suture revisited: A histological and immunohistochemical study using human fetuses

In human fetuses, the palatine process of the maxilla is attached to the inferior aspect of the horizontal plate of the palatine bone (HPPB). The fetal palatomaxillary suture is so long that it extends along the anteroposterior axis rather than along the transverse axis. The double layered bony palate disappears in childhood and the transverse suture is formed. To better understand the development of the double layered bone palate, we examined histological sections obtained from 25 fetuses of gestational age 9-11, 16-18 and 30 weeks. The double layered palate was seen in all of the specimens examined. Inferior angulation of the posterior end of the HPPB was evident at 9-11 weeks, but the initial palatine aponeurosis did not attach to the angulation but to a slightly anterior site. Both the maxilla and the HPPB were tightly attached to the vomer at 16-18 weeks. In both bones, bilateral plates met at the midline. The palatomaxillary suture was filled with short, randomly arranged collagen fibers. The nasal end of the suture was covered by a tight periosteum. Immunohistochemical examination of 3 fetuses at 16-18 weeks showed: 1) no expression of versican, tenascin-c or type II collagen in the suture; 2) few mitotic cells positive for proliferating cell nuclear antigen; 3) no or few CD34-positive developing vessels; and 4) no CD68-positive macrophages. These findings suggested that the fetal palatomaxillary suture was inactive for reconstruction and growth and that soft palate muscles likely did not contribute to the development of the double layered configuration.