Scanning electron microscopic study of the fibrous rings of the arterial orifices in embryos of the 7th and 8th weeks

The arterial fibrous rings were investigated in human embryos aged 7 and 8 weeks under light and scanning electron microscopes. In the present study it was shown that the arrangement of collagen and formation of fibres changes rapidly within one week. In the 7th week there are no collagen fibres and the netlike fibrils extend between processes of fibroblasts. At the end of the 8th week the collagen fibres are formed and they have different arrangements in the particular layers of the fibrous rings. (Folia Morphol 2010; 69, 3: 180-183

Development of the myelin sheath of the hypogastric nerves in a human foetus aged 23 weeks

The formation of the myelin sheath of the human hypogastric nerves was studied by electron microscopy in a foetus of 23 weeks of postovulatory age (220 mm C-R length). In the investigated foetus the hypogastric nerves were mainly composed of bundles of unmyelinated fibres. The myelinated fibres were seen to be at different stages of myelination. Well myelinated fibres had thick compact laminated myelin. The number of myelin lamellae on a single fibre was 22

Foramina on the internal aspect of the alveolar part of the mandible

Observations were made on 299 dry human mandibles and 21 autopsy heads. Foramina were observed in the inner surface of the alveolar part in 32% of the mandibles investigated. The diameter of the foramina varied between 0.4 mm and 1.6 mm. In most instances foramina were present between the lower medial and lateral incisors but in some cases they were also observed in the midline or between the lower lateral incisors and canines. Histological studies confirmed the presence of a neurovascular bundle in the accessory foramina. This bundle was formed by branches of the mylohyoid nerve, sublingual artery and accompanying veins

The length of the humerus in human embryos at developmental stages 18-23

The length of the humerus was measured in 69 staged human embryos at developmental stages 18-23 (7 and 8 weeks). It was found that the length of the humerus increases from 2.0 mm at stage 18 to 5.4 mm at stage 23. There were slight variations at certain of the stages investigated. Asymmetry between limb lengths was not found during the embryonic period under examination

Differentiation of the nuclear groups in the posterior horn of the human embryonic spinal cord

The formation of nuclear groups in the posterior horns of the human embryonic spinal cord was traced in serial sections of embryos of developmental stages 13 to 23 (32 to 56 postovulatory days). The following observations, new for the human, are presented: 1. The differentiation of the neural tube into 3 zones (germinal, mantle and marginal) is detected in the middle of the 5th week. 2. The primordia of the posterior horns are marked at stage 14 (33 days). 3. In the middle of the 7th week the nucleus proprius and substantia gelatinosa are discerned. 4. Differentiation of the nuclei within the posterior horns proceeds in the ventrodorsal and rostrocaudal gradients. (Folia Morphol 2011; 70, 4: 245–251

Early development of the human palate in stages 16 and 17

A study was performed on 12 human embryos at developmental stages 16 and 17 (6th week). In the investigated embryos the primary palate is formed from medial nasal, lateral nasal, and maxillary processes. The medial and lateral nasal processes merge and form the nasal fin at stage 16. This fin regresses and at stage 17 and persists as the oronasal membrane. The primordia of the secondary palate appear at stage 17. (Folia Morphol 2011; 70, 1: 29-32

Early trabeculation and closure of the interventricular foramen in staged human embryos

Internal differentiation of the ventricles was studied in staged serially sectioned human embryos of developmental stages 13-19 (postovulatory days 32-46). At stage 13 the trabeculation of both ventricles was advanced and the muscular part of the interventricular septum well marked. Dorsal and ventral endocardial cushions were fused and the atrioventricular canal was divided into two parts. In embryos at stage 18 the membranous interventricular septum was developing and the interventricular foramen was obliterated. At stage 19 the membranous part of the interventricular septum was becoming more cellular in structure. (Folia Morphol 2008; 67: 13–18

Schwann units in the human foetal phrenic nerve

In three human foetuses aged 15, 17, and 23 weeks the number of axons surrounded by single Schwann cells was counted. These Schwann cell/axon complexes form the Schwann units. The largest Schwann units in the foetus aged 15 weeks contained 232 axons, in the foetus of 17 weeks the number was 140 and in the foetus of 23 weeks the largest units contained 65 axons

Evidence that the caudal portion of the neural tube develops by cavitation of a neural cord in the caudal eminence of human embryos

The formation of the secondary neural tube was traced in serial sections of human embryos of developmental stages 13 to 17 (32-41 days after fertilisation). It was found that the secondary neural tube formation begins with cavitation of the neural cord. The minute cavities are seen in embryos at stages 13 and 15. At stages 16 and 17 the numerous cavities coalesce to form a single central canal

Skeletal units of the human embryonic mandible

The development of the mandible was traced on serial sections of 20 human embryos aged 5-8 weeks (developmental stages 13-23). Special consideration was given to the differentiation of skeletal units proposed by Sperber. The first skeletal units, namely the mandibular body, the alveolar unit and the condylar unit, may be distinguished in the 7th week. The primordia of all units are identified by the end of the embryonic period (8 weeks)