pointed to features of interest. the italian galeazzo di santa sofia made the first public dissection north of the alps in vienna in 1404. vesalius with a dissected cadaver in his de humani corporis fabrica, 1543 vesalius in the 16th century carried out numerous dissections in his extensive anatomical investigations. he was attacked frequently for his disagreement with galen's opinions on human anatomy. vesalius was the first to lecture and dissect the cadaver simultaneously. the catholic church is known to have ordered an autopsy on conjoined twins joana and melchiora ballestero in hispaniola in 1533 to determine whether they shared a soul. they found that there were two distinct hearts, and hence two souls, based on the ancient greek philosopher empedocles, who believed the soul resided in the heart. renaissance artists such as antonio del pollaiuolo studied anatomy to improve their artwork, as seen in this figurine of hercules, 1470 human dissection was also practised by renaissance artists. though most chose to focus on the external surfaces of the body, some like michelangelo buonarotti, antonio del pollaiuolo, baccio bandinelli, and leonardo da vinci sought a deeper understanding. however, there were no provisions for artists to obtain cadavers, so they had to resort to unauthorised means, as indeed anatomists sometimes did, such as grave robbing, body snatching, and murder. anatomization was sometimes ordered as a form of punishment, as, for example, in 1806 to james halligan and dominic daley after their public hanging in northampton, massachusetts. in modern europe, dissection is routinely practised in biological research and education, in medical schools, and to determine the cause of death in autopsy. it is generally considered a necessary part of learning and is thus accepted culturally. it sometimes attracts controversy, as when odense zoo decided to dissect lion cadavers in public before a "self-selected audience". britain body snatching headstone of an 1823 grave in stirling in britain, dissection remained entirely prohibited from the end of the roman conquest and through the middle ages to the 16th century, when a series of royal edicts gave specific groups of physicians and surgeons some limited rights to dissect cadavers. the permission was quite limited: by the mid-18th century, the royal college of physicians and company of barber-surgeons were the only two groups permitted to carry out dissections, and had an annual quota of ten cadavers between them. as a result of pressure from anatomists, especially in the rapidly growing medical schools, the murder act 1752 allowed the bodies of executed murderers to be dissected for anatomical research and education. by the 19th century this supply of cadavers proved insufficient, as the public medical schools were growing, and the private medical schools lacked legal access to cadavers. a thriving black market arose in cadavers and body parts, leading to the creation of the profession of body snatching, and the infamous burke and hare murders in 1828, when 16 people were murdered for their cadavers, to be sold to anatomists. the resulting public outcry led to the passage of the anatomy act 1832, which increased the legal supply of cadavers for dissection. by the 21st century, the availability of interactive computer programs and changing public sentiment led to renewed debate on the use of cadavers in medical education. the peninsula college of medicine and dentistry in the uk, founded in 2000, became the first modern medical school to carry out its anatomy education without dissection. united states a teenage school pupil dissecting an eye in the united states, dissection of frogs became common in college biology classes from the 1920s, and were gradually introduced at earlier stages of education. by 1988, some 75 to 80 percent of american high school biology students were participating in a frog dissection, with a trend towards introduction in elementary schools. the frogs are most commonly from the genus rana. other popular animals for high-school dissection at the time of that survey were, among vertebrates, fetal pigs, perch, and cats; and among invertebrates, earthworms, grasshoppers, crayfish, and starfish. about six million animals are dissected each year in united states high schools (2016), not counting medical training and research. most of these are purchased already dead from slaughterhouses and farms. dissection in u.s. high schools became prominent in 1987, when a california student, jenifer graham, sued to require her school to let her complete an alternative project. the court ruled that mandatory dissections were permissible, but that graham could ask to dissect a frog that had died of natural causes rather than one that was killed for the purposes of dissection; the practical impossibility of procuring a frog that had died of natural causes in effect let graham opt out of the required dissection. the suit gave publicity to anti-dissection advocates. graham appeared in a 1987 apple computer commercial for the virtual-dissection software operation frog. the state of california passed a student's rights bill in 1988 requiring that objecting students be allowed to complete alternative projects. opting out of dissection increased through the 1990s. in the united states, 17 states along with washington, d.c. have enacted dissection-choice laws or policies that allow students in primary and secondary education to opt out of dissection. other states including arizona, hawaii, minnesota, texas, and utah have more general policies on opting out on moral, religious, or ethical grounds. to overcome these concerns, j. w. mitchell high school in new port richey, florida, in 2019 became the first us high school to use synthetic frogs for dissection in its science classes, instead of preserved real frogs. as for the dissection of cadavers in undergraduate and medical school, traditional dissection is supported by professors and students, with some opposition, limiting the availability of dissection. upper-level students who have experienced this method along with their professors agree that "studying human anatomy with colorful charts is one thing. using a scalpel and an actual, recently-living person is an entirely different matter." acquisition of cadavers the way in which cadaveric specimens are obtained differs greatly according to country. in the uk, donation of a cadaver is wholly voluntary. involuntary donation plays a role in about 20 percent of specimens in the us and almost all specimens donated in some countries such as south africa and zimbabwe. countries that practice involuntary donation may make available the bodies of dead criminals or unclaimed or unidentified bodies for the purposes of dissection. such practices may lead to a greater proportion of the poor, homeless and social outcasts being involuntarily donated. cadavers donated in one jurisdiction may also be used for the purposes of dissection in another, whether across states in the us, or imported from other countries, such as with libya. as an example of how a cadaver is donated voluntarily, a funeral home in conjunction with a voluntary donation program identifies a body who is part of the program. after broaching the subject with relatives in a diplomatic fashion, the body is then transported to a registered facility. the body is tested for the presence of hiv and hepatitis viruses. it is then evaluated for use as a "fresh" or "prepared" specimen. disposal of specimens cadaveric specimens for dissection are, in general, disposed of by cremation. the deceased may then be interred at a local cemetery. if the family wishes, the ashes of the deceased are then returned to the family. many institutes have local policies to engage, support and celebrate the donors. this may include the setting up of local monuments at the cemetery. use in education human cadavers are often used in medicine to teach anatomy or surgical instruction. cadavers are selected according to their anatomy and availability. they may be used as part of dissection courses involving a "fresh" specimen so as to be as realistic as possible—for example, when training surgeons. cadavers may also be pre-dissected by trained instructors. this form of dissection involves the preparation and preservation of specimens for a longer time period and is generally used for the teaching of anatomy. alternatives some alternatives to dissection may present educational advantages over the use of animal cadavers, while eliminating perceived ethical issues. these alternatives include computer programs, lectures, three dimensional models, films, and other forms of technology. concern for animal welfare is often at the root of objections to animal dissection. studies show that some students reluctantly participate in animal dissection out of fear of real or perceived punishment or ostracism from their teachers and peers, and many do not speak up about their ethical objections. one alternative to the use of cadavers is computer technology. at stanford medical school, software combines x-ray, ultrasound and mri imaging for display on a screen as large as a body on a table. in a variant of this, a "virtual anatomy" approach being developed at new york university, students wear three dimensional glasses and can use a pointing device to " through the virtual body, its sections as brightly colored as living tissue." this method is claimed to be "as dynamic as imax ". advantages and disadvantages proponents of animal-free teaching methodologies argue that alternatives to animal dissection can benefit educators by increasing teaching efficiency and lowering instruction costs while affording teachers an enhanced potential for the customization and repeat-ability of teaching exercises. those in favor of dissection alternatives point to studies which have shown that computer-based teaching methods "saved academic and nonacademic staff time … were considered to be less expensive and an effective and enjoyable mode of student learning … contributed to a significant reduction in animal use" because there is no set-up or clean-up time, no obligatory safety lessons, and no monitoring of misbehavior with animal cadavers, scissors, and scalpels. with software and other non-animal methods, there is also no expensive disposal of equipment or hazardous material removal. some programs also allow educators to customize lessons and include built-in test and quiz modules that can track student performance. furthermore, animals (whether dead or alive) can be used only once, while non-animal resources can be used for many years—an added benefit that could result in significant cost savings for teachers, school districts, and state educational systems. several peer-reviewed comparative studies examining information retention and performance of students who dissected animals and those who used an alternative instruction method have concluded that the educational outcomes of students who are taught basic and advanced biomedical concepts and skills using non-animal methods are equivalent or superior to those of their peers who use animal-based laboratories such as animal dissection. some reports state that students' confidence, satisfaction, and ability to retrieve and communicate information was much higher for those who participated in alternative activities compared to dissection. three separate studies at universities across the united states found that students who modeled body systems out of clay were significantly better at identifying the constituent parts of human anatomy than their classmates who performed animal dissection. another study found that students preferred using clay modeling over animal dissection and performed just as well as their cohorts who dissected animals. in 2008, the national association of biology teachers (nabt) affirmed its support for classroom animal dissection stating that they "encourage the presence of live animals in the classroom with appropriate consideration to the age and maturity level of the students …nabt urges teachers to be aware that alternatives to dissection have their limitations. nabt supports the use of these materials as adjuncts to the educational process but not as exclusive replacements for the use of actual organisms." the national science teachers association (nsta) "supports including live animals as part of instruction in the k-12 science classroom because observing and working with animals firsthand can spark students' interest in science as well as a general respect for life while reinforcing key concepts" of biological sciences. nsta also supports offering dissection alternatives to students who object to the practice. the norina database lists over 3,000 products which may be used as alternatives or supplements to animal use in education and training. these include alternatives to dissection in schools. interniche has a similar database and a loans system.