Fetal head - displaying bones, fontanelles, and average measurements at 9 months of gestation
The fontanelles (or fontanels) of the fetal skull are critical anatomical features during vaginal birth. These allow the cranial bones to move around such that the newborn often resembles a Conehead right after birth - but the look is a good thing! The funky look usually goes away within the first day or two, and this weird pointy head is the primary reason that mom could push that watermelon-sized baby through a pelvic opening that could ordinarily not even accommodate a large mango.
The mastoid, sphenoidal, and posterior fontanelle generally disappear by six months of age, while the larger anterior fontanelle can take up to two years to grow into bone. A sunken fontanelle is one of the ways to tell if an infant is dehydrated.
An American Text-Book of Obstetrics. Edited by Richard C. Norris and Robert L. Dickinson, 1895.
Alveoli and Jaws Before the Appearance and After the Absorption of the Teeth
Fig 1. Alveoli of the adult upper jaw.
Fig 2. Upper jaw of aged individual after the loss of alveoli.
Fig 3. Alveoli of adult lower jaw.
Fig 4. Aged lower jaw, alveoli absorbed.
Fig 5 (center). Head of foetus, before appearance of alveoli.
Alveoli (trough, basin in Latin) in the skull are the hollows in which teeth sit. They’re surrounded by bony tissue, which grows the gums around the teeth.
When there are no teeth rooted in the jaws, the bony tissue recedes. When this happens due to injury, malformation, or old age, there is no anchor point for dental implants or bridges, so dentures or partial dentures must be used, instead.
The Anatomy, Physiology, and Pathology of the Human Teeth. Paul B. Goddard, aided by Joseph E. Parker, 1844.
Anatomy of a Fetal Giraffe
Proceedings of the General Meetings for Scientific Business of the Zoological Society of London. 1906.
Perinatal Osteogenesis Imperfecta (probably type II) and Blue Sclerae of OI
Osteogenesis imperfecta (OI), also known as brittle bone disease, is a set of disorders that involves the malformation or insufficient formation of collagen.
All types of this condition are genetic, and are present at birth. Types I through V are autosomal dominant, and Types VI through VII are autosomal recessive. Given the severity of types II and III, the fact that they’re autosomal dominant rarely comes into play.
Most variants of OI (but not type IV) display blue sclerae, which is one of the primary diagnostic criteria. X-rays showing multiple bone fractures in varying stages of healing are also common in OI, and the x-ray above shows many nodules where the ribs and arms have fractured during the antenatal period.
In the past, OI was often assumed to be rickets or osteomalacia, and in the modern era, child abuse is often suspected when symptoms aside from frequent fractures are not present.
A Text-Book of Pathology for Students of Medicine. J. George Adami and John McCrae, 1912.
Uterus with fetus at 8-months gestation
In this dissection you can see the three layers of the uterus: the endometrium, myometrium and perimetrium.
The endometrium is a layer of mucosal epithelial cells that is highly reactive to hormones. It’s the layer that provides the protective inner lining to the uterus before ovulation, allowing a fertilized egg to implant without harming the mother. If no fertilized egg implants, it is shed every 25-42 days, during the menstrual cycle. Sometimes, these cells escape beyond the uterus and grow within the abdominal cavity, causing a very painful condition called endometriosis.
The myometrium is the many layers of muscle cells that push the fetus out during birth. They’re triggered to contract by prostaglandins (specifically oxytocin) during menstruation and birth, and expel whatever is within the uterus.
Perimetrial cells are also known as the serosa, and surround the outside of the uterus. They’re epithelial cells that form a tough coating that provides a modicum of protection from things (such as bacteria or fungus) getting in from the perimetrial sac.
Image from Museum Vrolik via Morbid Anatomy
“Composition of five fetal skeletons”
“A composition of five fetal skeletons standing on a rock formation made
of kidney, bladder, and gall stones, with vascular trees. The uppermost
skeleton plays a violin with a bow made of dried arteries. The skeleton
on the left has a feather plume coming out of the top of its skull, and
the larger skeleton on the right has sheep intestine wound about its
pelvis and holds a spear made of adult vas deferens. The smaller
skeleton on the right holds a baton set with kidney stones. The skeleton
at the bottom lays on its back and holds a mayfly in its right hand“
Similar to the composition of three fetal skeletons, this composition of Frederik Ruysch was originally three-dimensional and composed of real materials gathered from cadavers. His daughter, Rachel Ruysch, helped assemble many of his displays. In creating these memento mori and anatomical curiosity displays, Frederik Ruysch also discovered and expounded upon several preservation and embalming techniques that were not widely known or had been forgotten by his time.
Thesaurus Anatomicus (tertius). Frederik Ruysch, 1721. Via The College of Physicians of Philadelphia Digital Library.
“A composition of three fetal skeletons”
Three fetal skeletons, between 6 and 8 months development, stand arranged on a display of renal, bladder, and gall stones, and vascular trees.
The topmost skeleton is that of a female at 6 months gestation, and holds a string of pearls. The left skeleton is a male at 7 months gestation, and holds a miniature scythe. The right one is a female at 8 months gestation, and is wiping its eyes with a sheet of mesentery - the connective tissue found between body cavities.
Thesaurus Anatomicus (Primus). Frederik Ruysch, 1721.
Skeleton of anencephalic fetus with complicated spina bifada
Cranial deformation is due to failure of skull to form bony material. Kerckringii proposes that this was an effect of the spina bifada.
Specilegium Anatomicum nec non Anthropogeniae Ichnographiam. Theodori Kerckringii, 1717.
Exencephaly, Pseudocephaly, and Anencephaly
In exencephaly, the brain is formed without the brain casing - the cranium. It is generally missing the forebrain (the prefrontal lobe), but is otherwise mostly formed. Despite this, the spinal cord is rarely formed with the brain, as there is a disconnect between the telencephalon and the hindbrain during very early development, and only the midbrain is formed.
In pseudoencephaly (a term rarely used in medicine nowadays), the midbrain and spinal cord are formed, but the forebrain is not.
In anencephaly, the most common of the three conditions, the brain and spinal cord are only tiny specs of what they should be. Curiously, despite them being a literal extension of the brain, the eyeballs sometimes fully form, though with no receptors to process the information they receive, even if the fetus were to survive, they would not see anything.
Human Monstrosities, Part IV. Barton Cooke Hirst and George A. Piersol, 1893.
Top: Uterine lining at 5 1/2 months, displaying thin maternal separation from fetus, and high level of placental implantation
Center: Relation of placenta to uterus at 5 weeks and 8.5 months
Bottom: Major arteries and veins of the placentaDid you know that the placenta is a temporary organ that’s actually created by the fetus, and not the woman?
The human female is a curious creature; like our close great ape cousins, but unlike almost all other mammals, they build up a thick barrier in the uterine wall, to protect against any potential embryo that might implant itself. When there’s no embryo implantation, the thickened wall is shed, in the process known as menstruation.
The thing is, most mammals don’t menstruate. They go into heat, and occasionally shed uterine lining (if the uterus is scratched, or an egg tries to implant but fails, for example), but there’s no regular cycle of bloody discharge relating to breeding. This is because other mammals go through triggered decidualization (developing a uterine lining only when a fertilized egg begins to implant itself), while the great apes (and a couple other convergently evolved families, including bats) experience spontaneous decidualization, where they develop a thick uterine lining during every ovulation, before an egg can even attempt to implant itself.
Why the different linings? Well, it turns out that there are three types of mammal placentas (remember, placentas are developed by the embryo/fetus, not the mother):
- Epitheliochordal, which is completely superficial, and does not connect in any significant way to the mother’s body. The endometrial epithelium, connective tissue, and uterine epithelium are all preserved and undisturbed in the mother. The fetus is separated from the mother by three layers of tissue. Nutrients and waste are delivered and eliminated through diffusion, rather than direct connection. This group includes equids, swine, and ruminants.
- Endotheliochordal, which is slightly more invasive to the mother, only preserves the uterine epithelium. Nutrients and waste are not exchanged through direct connection to the mother, but the placenta only leaves one layer of tissue between it and the mother. This group includes cats and dogs.
- Hemochorial is the most invasive form of placenta in the animal kingdom. The embryo directly hooks itself up to the host (mother’s) blood flow, and leaves no tissue layers between the female and the placenta. This allows much more efficient nutrient transfer to the embryo or fetus, but is also potentially the most harmful to the female since the embryo attaches itself so securely to the uterine wall. The female must develop preemptive measures (a thickened uterine lining) to protect herself from a life-form that is literally driven to take all of the nutrients it needs to develop, and which has adapted to connect itself directly to the host. This group includes elephant shrews, most bats, and most primates.
Interested in more about the science behind reproduction and how amazingly efficient the human embryo is at sucking its host clean, just to obtain its needed resources for development?
PZ Meyers at Pharyngula has an understandable explanation of the article I referenced for this post.
There is also a great site by R. Bowen about the pathophysiology of the reproductive system.
An American Text-Book of Obstetrics for Practitioners and Students. Edited by Richard C. Norris, 1895.
Anencephaly in the skeleton and whole fetus
Anencephaly is the congenital absence of the skull and neocortex, due to a neural tube defect between the 23rd and 26th day of pregnancy. At that point, the embryo is basically a tube with a thickened top, and when that top end doesn’t close properly, the part of the brain known as the telencephalon (the largest part of the brain, which includes the cerebral hemispheres and basically everything that allows us to experience the world and live life) doesn’t form, and because that doesn’t form, the skull above it isn’t triggered to form, either.
Anencephalic fetuses still develop some of the lower facial bones, the mandible, and the rest of their body, but the neural network of the spinal cord terminates at the brain-stem, and the condition is necessarily terminal, if the fetus even makes it to term. This is one of the few conditions that is often allowed to undergo late-term (generally second trimester) abortion - as these fetuses generally die in utero, and late-term fetal death is often very problematic in terms of infection and partial delivery, it’s much safer to induce labor and expel the fetus before this occurs.
Studies in mice have shown that folic acid supplementation (already common in females of child-bearing age) can drastically reduce one of the primary causes of anencephaly in humans (expression of the CART1 gene). However, as the condition is so rare in humans, and the supplementation of folic acid is already highly recommended to prevent other neural tube defects in fetuses (such as spina bifida), no studies with the same hypothesis have been, or will probably ever be, performed on humans.
Human Monstrosities, Part II. Barton Cooke Hearst and George A. Piersol, 1892.
Top: Uterine lining at 5 ½ months, displaying thin maternal separation from fetus, and high level of placental implantation
Center: Relation of placenta to uterus at 5 weeks and 8.5 months
Bottom: Major arteries and veins of the placenta
Did you know that the placenta is a temporary organ that’s actually created by the fetus, and not the woman?
The human female is a curious creature; like our close great ape cousins, but unlike almost all other mammals, they build up a thick barrier in the uterine wall, to protect against any potential embryo that might implant itself. When there’s no embryo implantation, the thickened wall is shed, in the process known as menstruation.
The thing is, most mammals don’t menstruate. They go into heat, and occasionally shed uterine lining (if the uterus is scratched, or an egg tries to implant but fails, for example), but there’s no regular cycle of bloody discharge relating to breeding. This is because other mammals go through triggered decidualization (developing a uterine lining only when a fertilized egg begins to implant itself), while the great apes (and a couple other convergently evolved families, including bats) experience spontaneous decidualization, where they develop a thick uterine lining during every ovulation, before an egg can even attempt to implant itself.
Why the different linings? Well, it turns out that there are three types of mammal placentas (remember, placentas are developed by the embryo/fetus, not the mother):
- Epitheliochordal, which is completely superficial, and does not connect in any significant way to the mother’s body. The endometrial epithelium, connective tissue, and uterine epithelium are all preserved and undisturbed in the mother. The fetus is separated from the mother by three layers of tissue. Nutrients and waste are delivered and eliminated through diffusion, rather than direct connection. This group includes equids, swine, and ruminants.
- Endotheliochordal, which is slightly more invasive to the mother, only preserves the uterine epithelium. Nutrients and waste are not exchanged through direct connection to the mother, but the placenta only leaves one layer of tissue between it and the mother. This group includes cats and dogs.
- Hemochorial is the most invasive form of placenta in the animal kingdom. The embryo directly hooks itself up to the host (mother’s) blood flow, and leaves no tissue layers between the female and the placenta. This allows much more efficient nutrient transfer to the embryo or fetus, but is also potentially the most harmful to the female since the embryo attaches itself so securely to the uterine wall. The female must develop preemptive measures (a thickened uterine lining) to protect herself from a life-form that is literally driven to take all of the nutrients it needs to develop, and which has adapted to connect itself directly to the host. This group includes elephant shrews, most bats, and most primates.
Interested in more about the science behind reproduction and how amazingly efficient the human embryo is at sucking its host clean, just to obtain its needed resources for development?
PZ Meyers at Pharyngula has an understandable explanation of the article I referenced for this post.
There is also a great site by R. Bowen about the pathophysiology of the reproductive system.
An American Text-Book of Obstetrics for Practitioners and Students. Edited by Richard C. Norris, 1895.
Museum Vrolik is one of the best non-US/UK medical museums around. The “open” collections barely comprise three medium-sized rooms, but those rooms are STUFFED with specimens, and researchers can gain access to an entire storeroom full of other specimens.
All of these are from genuine cadavers - no models or sculpting here.
Skiagraph (X-ray) of a dicephalus dibrachius
Using the roots “di-”, “-cephalus”, and “-brachius”, the description of this x-ray is made clearer:
Di-: two
-cephal-: pertaining to the head
-brachi-: pertaining to the arms
From these, a description of “two-headed two-arms” is now known.
Dicephalic dibrachius twins are also known as “dicephalic parapagus (dibrachial)”, with parapagus referring to the fused pelvis that is shared between the two.
Dicephalic parapagus twins can also be “tribrachial” (three-armed) or “tetrabrachial” (four-armed), depending upon how far down the torso the conjoining begins.
The Principles of Pathology. J. George Adami, 1912.