This current page gives a brief overview of late embryonic development (Carnegie stage 22) in the head and neck region when viewed in detail within specific regions.
Each highpower image has an equivilant low power image showing the region selected.
Stage 22 embryo and animation of head development (not to scale)
Page Links: Introduction | Overview | Hearing | Neck | Head Image Links |References | Search Pubmed | Glossary | Terms
B3 Transverse section of the stage 22 Head showing select regions shown in detail below.
Note the orientation (ventral top of image, dorsal bottom of image). The dark "pear-shaped" central structure at the top is the developing tongue. The two pale regions either side are the palatal shelves, note that they have not yet fused in the midline (failure of this process is cleft palate). Behind that a pale cartilagenous region (that later ossifies) encloses the structuctures of the inner ear, beside which middle ear bones are forming. On the righthand side of the head the external ear is visible. The lower half of the image shows the developing brainstem with a large ventricular space occupied in part by an extensive choroid plexus (manufacturer of cerebrospinal fluid).
Now look at the detailed images and descriptions below.
These selected images show the development of the inner and middle ear at this late embryonic stage.
Regions of stage 22 embryo head (mouth at top) in selected images of inner ear below
B5 Inner and Middle ear components.
Inner - Cross-sections of turns in the cochlear. Position of the spiral ganglia (auditory) laying adjacent to the duct. Large cavity of the utricle with the small saccule attached. Within the utricle the developing cristae ampullaris. Adjacent to the utricle a cross-section through a semi-circular canal.
Middle - the maleus, a middle ear ossicle. The developing tensor tympani muscle. The auditory tube (tubo tympanic recess) extending from the oral cavity towards the middle ear.
B6Cochlear Region
The differentiating wall of the organ of corti. The division of the VIII cranial nerve into a vestibular and auditory (spiral ganglia) component. The VIII cranial nerve exiting through the space known as the internal auditory meatus. The cartilage surrounding all these structures that will later ossify to form bone.
A7: Nasal septum. Vomeronasal organs. Hypophysis.
B1: Trigeminal ganglion and central root of trigeminal nerve.
B2: Neurohypophysis (infundibular part with hypothalamic recess of 3rd ventricle).
Residual lumen of Rathke's pouch, pars intermedia. Sphenoid cartilage.
B7,C1: Laryngeal caecum. Arytenoid swellings. Thyroid cartilage. L,R laminae and superior processes. Hyoid cartilage with sternohyoid muscles.
C2,C3: Tracheal epithelium. Note in C2, ventral tracheal cartilage. In C3 note rounded cells of hyaline tracheal cartilage, starting to push apart in central midline zone but compressed together at lateral margins. Thyroid gland.
C4: Tracheal epithelium (vacuolated) and trachealis muscle. Note regional changes in
cartilage as in C3 above. Oesophagus - epithelium (vacuolated), submucosa and muscularis externa with a few inner spiral and isolated, outer longitudinal muscle bundles.
C5,C6: Developing thymus.
Each highpower image has an equivilant low power image showing the region selected.
| A1 |
A2 |
A3 |
A4 |
A5 |
A6 |
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| A7 |
B1 |
B2 |
B3 |
B4 |
B5 |
B6 |
| B7 |
C1 |
C2 |
C3 |
C4 |
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This page is an overview of the structures visible within the head and neck of the late embryo at Carnegie stage 22.
Some details about head and neck development can be found in other sets of notes (hearing, endocrine, GIT). So do not consider this to be a detailed overview of the head at this stage.
Note the extensive differentiation of structures within the head and neck, but the relative inmmaturity of the brain.
Please email Dr Mark Hill if you wish to make a comment about this current project.