Paper - Perichondrial ossification and the fate of the perichondrium with special reference to that of the otic capsule

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Bast TH. Perichondrial ossification and the fate of the perichondrium with special reference to that of the otic capsule. (1944) Anat. Rec. 90(2): 139–148.

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This historic 1944 paper by Bast described fetal otic capsule development. Note that Bast, also had a series of related papers on the development of the otic capsule (1, 2, and 3).

Also by this author: Bast TH. Ossification of the otic capsule in human fetuses. (1930) Contrib. Embryol., Carnegie Inst. Wash. 121, Publ. 407, 53-82.

Bast TH. Blood supply of the otic capsule of a 150 mm (C.R.) human fetus. (1931) Anat. Rec. 48: 141-151.

Bast TH. Development of the Otic Capsule I. Resorption of the cartilage in the canal portion of the otic capsule in human fetuses and its relation to the growth of the semicircular canals. (1932) Arch. Otolaryng. 16:19

Bast TH. Development of the otic capsule II. The origin, development and significance of the fissula ante fenestram and its relation to otosclerotic foci. (1933) Arch. Otolaryng. 18(1):

Bast TH. Development of otic capsule III. Fetal and infantile changes in fissular region and their probable relationship to formation of otosclerotic foci. (1936) Arch. Otolaryng. 23: 509-525.

Bast TH. Perichondrial ossification and the fate of the perichondrium with special reference to that of the otic capsule. (1944) Anat. Rec. 90(2): 139–148.

Also by related authors: Anson BJ. Karabin JE. and Martin J. Stapes, fissula ante fenestram and associated structures in man: I. From embryo of seven weeks to that of twenty-one weeks (1938) Arch. Otolaryng. 28: 676-697.

Cauldwell EW. and Anson BJ. Stapes, fissula ante fenestram and associated structures in man III. from embryos 6.7 to 50 mm in length. (1942) Arch. Otolaryng. 36: 891-925.

Anson BJ. and Cauldwell EW. Stapes, fissula ante fenestram and associated structures in man: IV. From fetuses 75 to 150 mm in length. (1943) Arch. Otolaryng. 37: 650-671.


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Historic Embryology: 1880 Platypus cochlea | 1892 Vertebrate Ear | 1902 Development of Hearing | 1906 Membranous Labyrinth | 1910 Auditory Nerve | 1913 Tectorial Membrane | 1918 Human Embryo Otic Capsule | 1918 Cochlea | 1918 Grays Anatomy | 1922 Human Auricle | 1922 Otic Primordia | 1931 Internal Ear Scalae | 1932 Otic Capsule 1 | 1933 Otic Capsule 2 | 1936 Otic Capsule 3 | 1933 Endolymphatic Sac | 1934 Otic Vesicle | 1934 Membranous Labyrinth | 1934 External Ear | 1938 Stapes - 7 to 21 weeks | 1938 Stapes - Term to Adult | 1940 Stapes | 1942 Stapes - Embryo 6.7 to 50 mm | 1943 Stapes - Fetus 75 to 150 mm | 1946 Aquaductus cochleae and periotic (perilymphatic) duct | 1946 aquaeductus cochleae | 1948 Fissula ante fenestram | 1948 Stapes - Fetus 160 mm to term | 1959 Auditory Ossicles | 1963 Human Otocyst | Historic Disclaimer

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Perichondrial Ossification And The Fate of the Perichondrium With Special Reference to That of the Otic Capsule

T. H. Bast Department of Anatomy, University of Wisconsin, Madison

Four Figures


Perichondrial ossification for most so-called cartilage or long bones is well described in most text books of histology. Long cartilage bones are foreshadowed by a growing shaft-like model of cartilage. Such a cartilage model first appears in the mid region of the future bone. It increases in length gradually by multiplication of its cells toward the ends of the shaft. This process of cartilage cell multiplication continues until the individual has attained full growth. The shaft like model of cartilage in the young fetus is surrounded by a layer of compact mesenchyma (shown at left of fig. 3) which is known as the perichondrium. These cells in this perichondium which lie next to the cartilage may themselves become cartilage cells and thus slightly increase the diameter of the model in its early stages of development.

This augmentation in diameter is short lived as the center of the early cartilaginous model becomes quickly transformed into the diaphyseal ossification center with its enlarged lacuna and calcified matrix. This diaphyseal ossification center occurs in the early stages of the development of the cartilaginous model. Thus, new cartilage is forming at the ends of the model while the center is ossifying.

In response to this change in the cartilage model, the adjacent mesenchymal cells of the perichondrium metamorphose into osteoblasts which multiply rapidly and deposit osteoid tissue on the surface of the changed cartilage. This osteoid tissue quickly becomes calcified. These steps can be seen by reading figure 3 from left to right. With this transformation, the surrounding compact mesenchyme or developing fibrous tissue no longer surrounds cartilage but bone and is thus known as periosteum. Because of this, the generalized statement that the perichondrium becomes the periosteum as soon as the first perichondrial bone is formed has good morphological support and appears to be true for most bones. It is well to bear in mind that the transition from perichondrium to periosteum occurs at the time when it is still in a mesenchymal state and has not reached the stage of a specialized fibrous tissue.

The cartilaginous otic capsule and its perichondrium

The petrous portion of the temporal bone with its contained otic capsule is one of the cartilage bones. It differs from other bones in that it is neither a long bone nor a flat bone but rather a capsular or box-like bone enclosing the internal ear. The model or forerunner of this bone is the cartilaginous otic capsule. It makes its appearance in human fetuses of about 25 mm., crown rump length or at the age of 8 weeks. As the internal ear enlarges this capsule expands correspondingly. It remains cartilaginous until the internal ear has about attained its maximum size or at about the fourth or fifth month, after which the cartilage stops growing except at one or two minor spots and these are irrelevant to the question under consideration. The cartilage of the capsule therefore has attained its maximum growth before ossification begins.

The perichondrium during this period of growth and before ossification has set in, has begun to develop into a specialized capsular type of fibrous tissue. The innermost layer or two of cells next to the cartilage are somewhat rounded and resemble young cartilage cells. Outside of these the cells of the perichondrium become spread apart by the deposit of a collagenous fibrous matrix. The outermost part of the perichondrium retains more of its mesenchymal character. This is especially shown in the center picture of figure 4.

The advent of ossification and the fate of the perichondrium

Ossification centers appear in the cartilaginous otic capsule at various places. As many as fourteen such centers have been described. The ossification center, like those in other cartilage models, are characterized into the calcifying cartilage P.B., The fibrous layer transformed into perichondrial bone T.P.B., Trabeculae of perichondrial bone forming in the osteogenic layer by the enlargement of the lacunae and calcification of the matrix. The further transformation of the cartilage model has been previously described (Bast, ’30). Our attention here is directed to the formation of the perichondrial bone and the part played by tl1e perichondrium.

Fig. 1 Photomicrograph of a portion of the ossifying human otic capsule at the margin of the internal auditory meatus. (E. 38L —147 mm. (3.1%. — slide 23 - section 2 — Bast collection.)

Fig. 2 Photomicrograph of an area similar to that shown in the upper part of figure 1. -(E. 38L — 147 mm. 0.1%. - slide 22 - section 3. - Bast collection.)

Y.C., Young cartilage cell layer

F., Fibrous layer of perichondrium

0., Osteogenic layer of perichondrium

D., Dura

O.B., Osteogenic bud penetrating from the osteogenic layer through the ossifying fibrous layer

Perichondrial Ossification

Figures 1 and 2

The perichondrium overlying an ossification center exhibits three or sometimes four distinct layers.

1. The young cartilage cell layer. This layer may be one to three cells in thickness. This layer, consisting of young cartilage cells with some collagenous fibers between them, can be distinctly seen lying between the calcified cartilage matrix of the ossification center and the rest of the perichondrium. This layer quickly changes into mature cartilage a11d its matrix becomes calcified and it thus becomes part of the cartilaginous ossification center At the right in figure 2, this layer is seen as young cartilage whereas at the left, its matrix is being calcified.

In the development of most other cartilage bone, it seems to be this layer which metamorphoses into an osteoblastie layer the cells of which multiply rapidly to form the osteogenie tissue that deposits perichondrial bone (fig. 3).

2. The dense collaigcmlc layer. This layer of the perichondrium lies just outside the young cartilage cell layer. Its cells are spread apart and a dense matrix of collagenous fibers lies between them (figs. 1 and 2-F). This is the layer in wl1icl1 the first perichondrial bone is deposited. It is not clear whether some of the cells in this layer actually become osteoblasts and deposit bone about themselves orwhether the calcareous deposit is dependent on the osteogenie layer just outside of this layer.

3. The mesenchymal layer. This gives rise to two sheets of tissue, (a) the osteogenie layer and (b) the periosteum.

(a) The osteogenic layer arises from the mesenchymal layer just outside the dense collagenic layer (figs. 1, 2, 4-0). Many capillaries invade this area and the cells are transformed into osteoblasts. The function of this layer is twofold; one, to give rise to osteogenie buds which will perforate the underlying layer and invade the modified cartilage or ossification center, and two, to proliferate osteogenie tissue in situ and thus to give rise to the perichondrial bone. In areas where.peri— chondrial bone is being extensively formed, all of the mesenehymal layer may be transformed into this osteogenie layer (figs. 1 and 2, top).

(b) The periosteum as a rule develops from the outer part of the mesenchymal layer by the deposition of intercellular fibers. It overlies the osteogenie layer and the developing perichondrial bone (fig. 4). In Fig. 3 A panoramic View of part of a rib of a woodchuck (Mossman collection) which shows the transformation of the primitive perichondrium into perichondrial bone and into periosteum. At the extreme left is shown the primitive perichondrium (P) consisting of compact mesenchymal cells overlying the rib cartilage (0). Reading the picture from left to right, one sees the transformation of the deeper layer of the perichondrium into osteogenic tissue and osteoblasts. Near the middle of the picture, at O.T., osteoid tissue is forming on the surface of the cartilage. Other trabeculae of osteoid tissue seen forming in the osteogenic layer, at T.O.T. The dark staining osteobla.sts are lined up on the surface of these trabeculae. Toward the right the osteoid tissue is changed into bone. The periosteum (P.O.) is seen to be continuous with the original perichondriuin (P).

Fig. 4 This picture shows perichondrial ossification of the human petrous bone. (E. 36-L——135 mm. C.R.——slide 10, section 2 -—- Bast collection.) The small center picture shows the perichondrium (P) of thecartilagenous otic capsule. It is comparable to the perichondrium of figure three except that next to the young cartilage cells the layer is fibrous and not cellular. Both to the right and left, the picture shows various stages in the ossification process and the zoning of the perichondrium and its transformation into perichondrial bone and periosteum. F.—Fibrous layer. O.———0steogenic layer. P.0.——-Periosteum. O.B.—Osteogenic bud penetrating from osteogenic layer through the ossifying fibrous layer into the calcifying cartilage.

places where the mesenehyinal layer is all converted into osteogenic tissue, the periosteum later develops from the outer part of the osteogenic layer.


In the development of most cartilag'e bones, the cells of the perichondriurn which surround the carttilage model give rise to the osteo genic layer. The latter, in turn, forms the perichondrial bone. The outer, 1°eniai11i‘11g portion of the peroehondrium becomes the periosteum of the perichondrial bone.

In case of the petrous bone, the periehondrium of the otic capsule gives rise in its deeper part to a dense C0ll.a.g"€11lC layer which forms the basic tissue in which the first perichondrial bone is deposited. Most of the rest of the periehondrium gives rise to the ostyeogenic tissue which is primarily responsible for the forination of the perichondrial bone.

Only the outer part of the original perichondrium becomes the permanent periosteum.

Cite this page: Hill, M.A. (2024, April 12) Embryology Paper - Perichondrial ossification and the fate of the perichondrium with special reference to that of the otic capsule. Retrieved from

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