The rhomboid fossa is a
rhombus-shaped depression that is the anterior part of the
fourth ventricle. Its anterior wall, formed by the back of the
pons and the
medulla oblongata
The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (involun ...
, constitutes the floor of the fourth ventricle.
It is covered by a thin layer of
grey matter continuous with that of the
spinal cord; superficial to this is a thin lamina of
neuroglia
Glia, also called glial cells (gliocytes) or neuroglia, are non-neuronal cells in the central nervous system (brain and spinal cord) and the peripheral nervous system that do not produce electrical impulses. They maintain homeostasis, form mye ...
which constitutes the
ependyma of the ventricle and supports a layer of ciliated
epithelium
Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellul ...
.
Parts
The fossa consists of three parts, superior, intermediate, and inferior:
;The superior part
:The superior part is triangular in shape and limited laterally by the
superior cerebellar peduncle
In the human brain, the superior cerebellar peduncle (brachium conjunctivum) is a paired structure of white matter that connects the cerebellum to the midbrain. It consists mainly of efferent fibers, the cerebellothalamic tract that runs from a cer ...
; its apex, directed upward, is continuous with the
cerebral aqueduct; its base is represented by an imaginary line at the level of the upper ends of the superior foveae.
;The intermediate part
:The intermediate part extends from this level to that of the horizontal portions of the
taeniae of the ventricle; it is narrow above where it is limited laterally by the middle peduncle, but widens below and is prolonged into the
lateral recesses of the ventricle.
; The inferior part
:The inferior part is triangular, and its downwardly directed apex, named the ''calamus scriptorius'' (as is shaped like a writing quill-nib)
is continuous with the central canal of the closed part of the medulla oblongata.
The
sulcus limitans forms the lateral boundary of the
medial eminence.
Features
In the superior part of the rhomboid fossa it corresponds with the lateral limit of the fossa and presents a bluish-gray area, the
locus coeruleus
The locus coeruleus () (LC), also spelled locus caeruleus or locus ceruleus, is a nucleus in the pons of the brainstem involved with physiological responses to stress and panic. It is a part of the reticular activating system.
The locus coerule ...
, which owes its color to an underlying patch of deeply pigmented nerve cells, termed the
substantia ferruginea
The substantia ferruginea is an underlying patch of deeply pigmented nerve cells located in the floor of the superior part of the sulcus limitans.
It was coined in 1838 and 1851.
See also
* Rhomboid fossa
* Sulcus limitans
* Locus ceruleus
* Fo ...
.
At the level of the
facial colliculus the sulcus limitans widens into a flattened depression, the superior fovea, and in the inferior part of the fossa appears as a distinct dimple, the
inferior fovea
Inferior may refer to:
* Inferiority complex
* An anatomical term of location
* Inferior angle of the scapula, in the human skeleton
* ''Inferior'' (book), by Angela Saini
* ''The Inferior'', a 2007 novel by Peadar Ó Guilín
See also
*Junior ( ...
.
Lateral to the foveæ is a rounded elevation named the area acustica, which extends into the lateral recess and there forms a feebly marked swelling, the tuberculum acusticum.
Winding around the inferior peduncle and crossing the area acustica and the medial eminence are a number of white strands, the striæ medullares, which form a portion of the cochlear division of the acoustic nerve and disappear into the median sulcus.
Below the inferior fovea, and between the
hypoglossal trigone and the lower part of the area acustica is a triangular dark field, the
vagal trigone, which corresponds to the
sensory nucleus of the vagus and
glossopharyngeal nerves
The glossopharyngeal nerve (), also known as the ninth cranial nerve, cranial nerve IX, or simply CN IX, is a cranial nerve that exits the brainstem from the sides of the upper medulla, just anterior (closer to the nose) to the vagus nerve. B ...
.
The lower end of the vagal trigone is crossed by a narrow translucent ridge, the
funiculus separans
The cells of the dorsal nucleus of vagus nerve are spindle-shaped, like those of the posterior column of the spinal cord, and the nucleus is usually considered as representing the base of the posterior column. It measures about 2 cm. in length ...
, and between this
funiculus and the
gracile nucleus
In neuroanatomy, the dorsal column nuclei are a pair of nuclei in the dorsal columns in the brainstem. The name refers collectively to the cuneate nucleus and gracile nucleus, which are present at the bottom of the medulla oblongata. Both nucl ...
, is a small tongue-shaped area, the
area postrema.
On section it is seen that the funiculus separans is formed by a strip of thickened ependyma, and the area postrema by loose, highly vascular, neuroglial tissue containing nerve cells of moderate size.
Additional images
File:Gray719.png, Hind- and mid-brains; postero-lateral view.
File:Gray785.png, Figure showing the mode of innervation of the Recti medialis and lateralis of the eye.
File:Human caudal brainstem posterior view description.JPG, Human caudal brainstem posterior view
References
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Ventricular system