Anamorphic skulls, a head made of blood, the morbid sensibilities of the pre-Raphaelites and the last days of Richelieu. Richard D North goes on a funereal procession through the major London exhibitions but finds, as the seasonal excesses move into high gear, that he has plenty to smile about.
You would think it was Easter coming, not Christmas. London is awash with images of death and the vanity of human life. We have a severe case of de rigueur mortis. It'll do us good, mostly.

Thomas More wrote that a day is wasted in which there has been no remembrance of death. Contemplating death informs the way we live our lives in rather the way that a fullstop reverse-engineers discipline into the half-formed order of the words which precede it. Vanitas painting - work which dwells on the vanity of human desires - has a long history in still-lives, in portraiture and in allegorical work. The skull is a standard medieval icon, often inscribed with the words, Memento mori, remember that you have to die. But it would be wrong to look at the skull in the gleaming Holbein double portrait of The Ambassadors at the National Gallery as a talismanic, still less merely a totemic, medieval image. Though conveniently compressed, this must be more than a tactful gesture to convention. The anamorphosis which distorts the skull allows its intimation of mortality to have a role which is both central and ambiguous. Surely the anamorphosis has been designed to say that life is lived with death as a major factor whose reality we suppress, but which is occasionally and usefully glimpsed in its real perspective?

Thinking about mortality is not necessarily morbid. Susan Foister, one of the curators of the show, points out: "The skull is there to remind one of mortality, but the Cross is there, too, and it is best seen from the same position that restores the skull to normality. So beyond mortality, there is eternal life."

The ambassadors, with the Cross alongside their scientific and astronomical instruments, are religious but humanist, and their understanding of the world is similarly on the cusp between the classical and the modern. But the Vanitas tradition remained intact through the centuries of rationalism, which in any case produced their own reaction to conscious materialism. G F Watts has a funeral bier, with a shrouded corpse and the cast-off armour of a busy worldly life, in his 1890s Sic Transit, displayed now in the "Symbolism in Britain" show at the Tate. Watts saw the vanities of the world in a socialist light, but the message written on the painting ("What I spent, I had; What I saved, I lost; What I gave, I have") is about charity not taxation, and is borrowed from a 15th century tomb.

The Victorians enjoyed morbidity: the Wallace Collection is showing-off paintings by Paul Delaroche under the title, "Death and Devotion". One of the offerings has a particularly Vanitas sub-text: it shows the sickly Richelieu in a barge towing an aquatic tumbril containing two aristocratic would-be regicides on the way to execution. Richelieu, for all his grandeur, was barely to outlive his victims, and the curator of the show argues that the vignette satisfied its period as a reminder that there was to be a revolutionary comeuppance to the vanities of monarchical absolutism.

The Symbolists remind us that the Medievalist fantasy had a dark side. Sir Joseph Noel Paton's erotic sprite in The Pursuit of Pleasure: A vision of human life in the "Victorian Fairy Painting" at the Royal Academy, gives us further clear evidence that the 19th century was as interested as any in sin and its wages.

The pre-Raphaelite and the fairy shows share an interest in our expression and suppression of the shadowed and sinful worlds within. They are often lovely, but are arguably about allegory taken to the point of evasion. The "Sensation" show, in amazing juxtaposition next door to the fairies, is arguably about confrontation taken to the point of derision.

"Sensation" is solidly in the vanitas tradition. True, Damien Hirst's preoccupation with animals hangs over the exhibition, and us all. Animals also preoccupy the grand old man of shock, the Austrian Hermann Nitsch, at the 30, Underwood Gallery. Nitsch has worked in animal blood for thirty- odd, very odd, years. But the animality of humans, our assumption of our difference from animals, and the moral charge of our supposed abuse of animals are all relevant to thinkers and artists much more because of what they say about our hubris, than what they say about animals. Nitsch's show is rich in altars and crucifixions: it is one long Stations of the Cross, perhaps the very cross.

"The Quick and the Dead" show, just closed at the Royal College of Art, was a meditation on mankind's enduring interest in human flesh becoming meat. But post-Renaissance and Enlightenment as much of the work was, the artists often made their skeletons and flayed figures into Vanitas images, some very directly, as in the case of Hogarth. You got the feeling that both artist and surgeon were wondering where the soul might reside in the carcass.

The "Sensation" show, which has some of the "Quick and the Dead" artists, seems everywhere to conclude that nothing so glorious can be found anywhere. That makes it nervously jokey, or properly realistic, according to your point of view. There is a rather disturbing technical mastery in much of the work. And who is to say that Marc Quinn's Self, a blood and metal skull held together by refrigeration, is not as good and serious a Mementi mori as Holbein's? In one room at the Academy, one can even see Myra Hindley's head subjected to anamorphosis in Cerith Wyn Evans' concave mirror, Inverse, Reverse, Perverse. Of course, the difference is that the historic tradition used shock-tactics - the sensation of disgust - as instrumental in a moral purpose which artist and observer both understood. One could use the word sublime of the older stuff, as Edmund Burke intended.

The skilled portraitist Tom Phillips would not accept that "Sensation" is trivial. As a senior Royal Academician, he helped concoct the show, and has made works which could have appeared in it. At the Dulwich Picture Gallery, Phillips' new show is much concerned with death, evidenced in his series of collages on Dante's Inferno. His skulls, a few of which are assembled here, are a tabula rasa on which to write and paint: their shape is preserved, but they are metaphorically turned inside out as we eavesdrop on the thoughts within. Phillips - a literary man - has made and painted Crosses built out of words, and both skulls and crucifixes are uplifting. They are placed in superb proximity to the mausoleum made by Sir John Soane to be an integral part of the picture gallery. It is very fitting that an entire building intended as a vanitas should now house a modern show of work largely about death, but not above being moral and charming with it.

All in all, we have plenty of material with which to combat the bad side of Christmas: its sugariness, and materialism. Its excess, however, some of these shows can easily match.

Holbein's Ambassadors is the 'Making and Meaning' show at the National Gallery, until February 1, 1998. 0171 839 3321. 'The Age of Rossetti, Burne-Jones & Watts, Symobolism in Britain, 1860-1910', is at the Tate until January 4, 1998. 0171 887 8000. 'Death and Devotion: Paintings by Paul Delaroche' is at the Wallace Collection, Manchester Square, W1, until February 2 1998. 0171 935 0687. 'Victorian Fairy Painting' is at the Royal Academy of Arts until February 8, 1998. 0171 300 8000. 'Sensation' is at the Royal Academy of Arts until December 28. 0171 300 8000. 'Hermann Nitsch: Orgy, mystery, theatre', at 30 Underwood St Gallery, 1pm-6pm, Friday, Saturday and Sunday, until January 27 1998. 0171 336 0884. 'Tom Phillips: Drawing to a Conclusion', at the Dulwich Picture Gallery, College, London SE21 7AD, until January 18 1998. 0181 693 5254.