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The lacrimal bone is a small bone in the medial orbital wall associated with the lacrimal drainage region. Its position contributes to the space around the lacrimal sac. It is structurally distinct from the secretory lacrimal gland despite the shared name.

Larry L. Hench (1938–2015) was a materials scientist known for developing bioactive glass: a biomaterial designed to form a bond with living bone. The National Academy of Engineering memorial records his name, dates and contribution to bioactive glasses and glass corrosion.^[ref]

His own account explains the key experimental observation: early glass specimens implanted in rat femurs became bonded to bone. The scientific question was how the solid’s composition and its reactions with body fluid could create that interface. The proposed mechanism involved dissolution and formation of a mineral-rich surface layer, followed by biological attachment.^[ref] The earlier joint paper compared solubility and interfacial hydroxyapatite crystallization studies with implant histology and ultrastructure.^[ref]

This work changed the design question from simply finding a strong solid to understanding a solid–tissue system. A bond at the interface and sufficient bulk strength are distinct properties: a strong implant can still detach at its surface, while a bonded but weak material can fail internally. Testing where a loaded specimen separates helps distinguish these possibilities. That distinction connects Hench’s experimental approach to biocompatibility, biomechanics and tissue engineering.

A limb digit is one of the terminal rays of a tetrapod limb, such as a finger or toe. A digit includes a series of phalanges and surrounding tissues; it is not synonymous with one phalanx. Several bones can therefore belong to one digit, with a joint connecting successive elements.

Counting digits and counting their component bones answer different questions. If a hypothetical limb has five digits and each has three phalanges, it has five digital rays but fifteen phalangeal bones. This deliberately simplified example shows why an isolated row of bones must first be reconstructed into its anatomical arrangement before it is used to infer digit number.

Nor is five digits the defining ancestral condition of every early tetrapod limb. In 1990, fossil descriptions documented eight digits in the forelimb of Acanthostega, while other early specimens had different counts. These observations challenged reconstructions that began by assuming an originally fixed five-element pattern. The specimens are evidence about the early diversity of limbs, rather than abnormal individuals judged against the human hand.^[ref]

A dermal skeleton organized into relatively large plates or bones, contrasting with a covering dominated by small separate scales or odontodes.

The maxilla is a major upper-jaw bone contributing to the upper dental arch, hard palate, nasal region and orbit. Its several processes connect these regions structurally. The term refers to the bone, rather than all soft tissues of the upper jaw.

M. D. Morris, or Michael D. Morris, is a chemist whose research connects Raman spectroscopy and chemical imaging with the composition and mechanics of bone and other tissues. His University of Michigan profile describes both instrument development and image processing for spectroscopic contrast.^[ref]

A central idea is to retain a Raman spectrum at each sampled position instead of recording only brightness. A map of a phosphate band can then emphasize mineral, while a different spectral contribution carries information about protein. Morris and W. F. Finney also studied how bone spectra respond during controlled elastic loading.^[ref]

As an original two-channel example, suppose reference responses for mineral and an organic component give measured intensities $I_1=2a+b$ and $I_2=a+3b$. Measurements $(I_1,I_2)=(5,5)$ yield $a=2$ and $b=1$ by solving the linear system. These are model response coefficients, not automatically mass fractions: quantitative composition additionally requires suitable reference specimens and measurement calibration. The example shows why spectral information can separate contributions that a single brightness image mixes.

Megalosaurus is a genus of extinct predatory theropod dinosaurs known from Jurassic remains in England. Fossil jaw and limb material from Stonesfield contributed to its early recognition. William Buckland published a description in 1824, before the later name Dinosauria had been introduced. ^[ref]

The preserved lower jaw illustrates how specific observations constrain reconstruction. Serrated, blade-like teeth support a meat-eating interpretation, while imaging can reveal replacement teeth hidden within the bone. A fossil specimen and a complete life reconstruction contain different amounts of direct evidence: posture, missing anatomy and evolutionary relationships require comparisons beyond the isolated jaw.

A metacarpal is a bone of the hand between the carpal region and a digit’s proximal phalanx. The series forms much of the palm’s skeletal framework. Different mobility at its proximal connections contributes to the distinct roles of the thumb and other fingers.

Mineralized tissue is biological tissue in which mineral forms a substantial structural component of an organic matrix. Bone, dentine and enamel are familiar examples, but they differ markedly in composition and architecture. In bone, mineral based on hydroxyapatite is associated with a collagen-rich extracellular matrix; biological cells form and maintain that matrix. Mineralization describes a material feature, not the absence of living activity.^[ref]

A mineralized tissue is therefore also a biological composite material. Mineral amount, organic matrix, water, porosity and orientation can each affect the response. The Young's modulus of an entire specimen cannot be inferred from mineral content alone: constituent geometry changes load sharing, just as it does in the isostress rule of mixtures and the longitudinal rule of mixtures. These ideal mixture models clarify the role of geometry without being exact models of a real bone.

Even the phrase “mineral fraction” needs a specified measurement. Consider a hypothetical dry two-component specimen with $6\mathrm{mg}$ of mineral of density $3.0mg/m{\mathrm{m}}^3$ and $4\mathrm{mg}$ of organic material of density $1.3mg/m{\mathrm{m}}^3$. Its mineral mass fraction is $0.60$, but its mineral volume fraction isThese chosen numbers describe a bookkeeping example, not a measured tissue composition. Adding water or pores changes which total volume belongs in the denominator. A mechanical mixture calculation needs the appropriate volume fractions, not a mass percentage silently substituted for them.

An instructive primary structural study examined elephant ivory, a form of dentine, with complementary X-ray scattering, polarized-light microscopy and scanning electron microscopy. The investigators found that mineralized collagen orientations differed between the outer and inner parts of the tusk, including an outer wrapping orientation and a predominantly axial, plywood-like arrangement farther inside.^[ref] The result motivates combining methods: a bright pattern in polarized light, an electron-microscope image and a scattering pattern provide different evidence about the same organized mineralized tissue. Observing orientation is not by itself a direct measurement of its full mechanical constitutive equation.

An Early Devonian Mongolian jawed vertebrate whose braincase contains a trabecular internal tissue interpreted as endochondral bone. Implications for ancestral bone depend on both tissue identity and phylogenetic placement.

The branch of surgery concerned with the musculoskeletal system. It connects bones, joints, tendons and associated tissues with the restoration or preservation of mechanical function.

Formation of bone. Dermal, perichondral and endochondral modes should be distinguished from mineral deposition in cartilage.

A disorder involving changes in the whole anatomical joint, including cartilage, bone and surrounding tissues. It is more than a passive wearing away of cartilage and differs mechanistically from autoimmune rheumatoid arthritis.^[ref]

An inflammatory or injury-related disorder involving bone and adjacent cartilage. The exact named condition matters because historical and modern uses do not identify one uniform mechanism.

Osteology is the study of bones, including their structure, development, variation and relations. It connects individual landmarks to the mechanics of joints and muscle attachment. Comparative osteology also supplies characters for paleontology and reconstruction of evolutionary relationships.

A bone contributing to the palate.

Proliferating inflammatory tissue that extends over a surface, particularly synovial tissue in rheumatoid arthritis. At a joint it can contribute to cartilage and bone damage through an active tissue process.

A parietal bone forms much of the superior and lateral cranial vault. The paired bones meet near the midline and join other skull bones through sutures. Their broad surfaces contribute protection while the junctions have distinct developmental relationships.

The New Head hypothesis offers a plausible developmental explanation for vertebrate cranial innovation: migratory neural crest biological cells helped build a feeding and sensory apparatus that could diversify. Its strongest form is a hypothesis about integration of several innovations, not a claim that neural crest alone produced every part of the vertebrate head or directly proves evolutionary success.

neural crest arises near the border of the neural and non-neural ectoderm. Cells undergo an epithelial-to-mesenchymal transition, migrate and generate diverse derivatives. Cranial populations contribute substantially to facial and pharyngeal cartilage, bone and connective biological tissues; other populations supply peripheral neurons, glial cells and pigment biological cells. These are regionally restricted potentials, not a claim that every crest biological cell makes every derivative. Importantly, neural crest remains ectodermal in origin even when it makes biological tissues often associated with mesoderm.

The hypothesis proposed by Carl Gans and R. Glenn Northcutt linked the new head to a transition from passive suspension feeding toward more active food acquisition, with an expanded cranial skeleton, sensory systems and muscularised pharyngeal apparatus. neural crest, ectodermal placodes and mesodermal muscle contributions were complementary. A support skeleton allows feeding surfaces and sensory organs to be positioned; sensory organs guide action; muscles supply force. Their integration gives a more convincing functional explanation than a list of crest derivatives alone.^[ref]

Several distinctions keep this argument anatomically accurate. The brain largely develops from the neural tube; ectodermal placodes contribute important cranial sensory components; much cranial muscle comes from mesoderm. neural crest provides connective and skeletal organisation around those biological tissues and contributes to their interactions. The pharyngeal arches are multicellular constructions involving neural crest, mesoderm, ectoderm and endoderm. Thus loss of cranial neural crest can secondarily disrupt biological tissues it does not itself become. Fate mapping distinguishes cellular contribution, while selective ablation and rescue test developmental necessity and interaction.

There is direct experimental support for a role in diversification. Reciprocal cell transplantation of prospective beak neural crest between quail and duck shifted beak morphology toward the donor species and altered nearby host biological tissues. This connects intrinsic properties of the crest population with instructions to its environment, explaining how changes in one interacting population can reshape a complex organ. Same-species grafts, developmental-stage matching and permanent donor labels are needed to distinguish patterning information from surgical effects or simple replacement. The result supports a mechanism for morphological variation; it does not by itself establish which ancestral feeding behaviour was favoured by natural selection.^[ref]

Comparative evidence also qualifies an abrupt invention narrative. Neural-border regulatory and sensory programmes have antecedents outside vertebrates. In Ciona, a pigment-cell lineage with parts of a crest-like regulatory programme can acquire migratory behaviour after experimental manipulation. Such a rudiment supports stepwise assembly of properties; a migrating pigment precursor is not automatically equivalent to the full multipotent, skeletogenic vertebrate neural crest. Compare origin, regulatory dependencies, migration and derivative range separately.^[ref]

Jawless vertebrates are another important logical control. Their existence prevents equating the origin of neural crest with the later origin of jaws: cranial contributions preceded the particular jawed-vertebrate feeding apparatus. Later modifications of an inherited developmental system can support new structures without repeating its original evolutionary origin. Conversely, retention of homologous genes does not establish identical biological cell types; comparative experiments must test how those genes interact and what the biological cells actually produce.

A strong research programme would combine lineage tracing and selective perturbation across vertebrate and non-vertebrate chordates, compare homologous regulatory elements and ask whether reconstructed changes alter migration, skeletal competence or biological tissue interactions. Fossils constrain when hard cranial structures appeared, but rarely identify the embryonic source directly. Modern ablation establishes a present-day requirement, not the sequence of ancestral events. Likewise, species richness is influenced by many ecological and historical factors, so it is not a direct experimental readout of one developmental innovation.

The defensible conclusion is that neural crest supplied a versatile developmental substrate for cranial construction and diversification, acting with placodes and other biological tissues. Experimental grafting and comparative developmental evidence make that causal contribution substantial. The specific ecological transition proposed in the New Head hypothesis remains an evolutionary reconstruction whose details require evidence beyond the existence of crest derivatives.

The expected historical picture is a hard, infiltrating breast tumour, often initially painless, followed variably by local tethering, lymphatic spread, ulceration and distant disease. “Scirrhus” describes a fibrous pattern of carcinoma, not a complete modern subtype. A soft or painless lump cannot thereby be excluded from breast cancer, and a hard lump alone is not proof of it.

The person may notice a small firm lump or an altered contour before experiencing substantial discomfort. An irregular hard mass can become less mobile as it involves surrounding tissues. Skin dimpling, tethering or puckering, nipple retraction, altered nipple discharge and enlargement of axillary lymph nodes are important associated findings. Later local disease may fix the breast to deeper structures, ulcerate, bleed or produce malodorous discharge. Pain can be lancinating or persistent, but waiting for pain is unsafe because early breast cancer often causes none.^[ref]

The course varies over months or years; not every sign appears in sequence. Local growth can coexist with initially good general health. Subsequent metastasis may affect bones, lungs, liver or other organs and cause symptoms distant from the breast. Historical observers could recognize recurrence after apparently complete removal without possessing modern staging or receptor classification. A temporary reduction in pain, apparent softening or improved appetite did not establish elimination of malignant tissue.^[ref]

In an 1866 decision, reasons favouring operation included a localized lesion that could apparently be removed, reasonable general strength, no evidence of distant dissemination and willingness to accept the considerable contemporary risks. The prospect of effective local removal argued against waiting for ulceration and exhaustion. Extensive fixation, very widespread nodal or skin involvement, distant disease, severe intercurrent illness or a risk disproportionate to expected benefit argued against an attempted curative removal. Axillary findings needed assessment rather than a simplistic rule that any enlarged node either guaranteed or prohibited success. Palliation and the woman's preferences remained relevant even when cure was implausible.

Treatment other than removal had included local protection or compression, dressings for ulceration and bleeding, analgesia, dietary or tonic measures and destructive chemical applications. A 1865 clinical text records plasters, iron, cod-liver oil and treatment directed at ulcer discharge and haemorrhage. Those are observations of symptomatic management, not proof of tumour eradication.^[ref] Contemporary discussion also proposed caustics or injections of chemicals such as zinc chloride, sometimes after cutting or removing tissue. These methods could damage tissue and relieve or alter a surface lesion without demonstrating durable control of the whole disease. They should not be represented as effective alternatives to evidence-based treatment.^[ref]

Modern correction: establish tissue diagnosis and stage, then plan local and systemic treatment together. Clinical examination and appropriate breast imaging lead to a core needle biopsy or another indicated sampling method. Histology, extent of disease and relevant biomarkers guide management; “scirrhous” appearance cannot substitute for these. Axillary assessment forms part of pretreatment evaluation.^[ref] Depending on the cancer and circumstances, treatment may include breast-conserving surgery with appropriate radiotherapy, mastectomy, systemic treatment before or after surgery, endocrine therapy or targeted therapy. Some locally advanced disease needs systemic treatment before a surgical decision, so the historical judgement “fixed, therefore never operable” is not a universal modern rule.^[ref] For advanced disease, treatment also addresses pain, wound problems and other symptoms. Palliative benefit is a valid aim, but must be distinguished from a claim of cure.